IT is a spectacle that has almost become as much a part of Westminster life as the state opening of Parliament.

Shame-faced MPs shielding their eyes from the press pack after being lured into boasting about selling their services to private companies.

First they reject the charges of conflict of interest with indignant protestations of innocence; then they blame the rules and say everyone does it; then they end up end crawling out of the Palace of Westminster to an ignominious retirement.

Yes, I know it's hard to feel sympathy for these politicians, but really it is a tragic story. I've seen two generations of politicians enter Parliament since I started in political journalism 30 years ago and I've seen most of them start out full of enthusiasm and high ideals, determined to put the world to rights.

I can honestly say I have never met an MP who went in to politics to make money. Mostly they enter politics because they believe strongly in certain ideas and want to change society.

Take Jack Straw, who was disgraced last week after being secretly filmed apparently saying he had used his influence to change EU rules on behalf of a private company. He began as a hirsute student radical in the 1970s; a veteran of university occupations. He worked for the left-wing TV programme World In Action before entering parliament where he established himself as a radical voice especially on civil liberties and parliamentary reform. He was responsible for the Freedom of Information Act and the equalisation of the age of consent for gay people.

Then he entered the front rank and things began to change. By the time he was Foreign Secretary under Tony Blair in 2002 he had become a pro-American hawk eagerly preparing the ground for the Iraq war. It was downhill all the way to his £5,000 a day consultancy habit revealed last week.

Malcolm Rifkind, who also fell on his sword last week after the same Daily Telegraph/Channel 4 sting, was never a student radical. But he did stand for a very decent, reformist form of Scottish Conservatism. I recall his battles against the ultra-Thatcherite Michael Forsyth back in the 1980s. I also remember him intervening in 1987 to stop Special Branch from arresting and incarcerating BBC Scotland colleagues after the Secret Society programme had revealed the existence of a British spy satellite programme.

What happens to them? Well, during their careers, politicians become exposed to many very important people - businessmen, university principals, quango-crats, BBC bosses - who all seem to earn vastly more than they do. The average chief executive of a FTSE 100 company earns more than £4m a year. The Director General of the BBC is on £600k and even many local authority directors earn more than the Prime Minister. MPs think to themselves: what's wrong with me that I don't get similar reward?

Of course, the reason they don't get big money is that they are, well, politicians. They are holders of office by virtue of being elected by the ordinary people of Britain who don't earn anything like the £67,000 that is the MP's basic wage (plus expenses of course - but let's not go there).

To represent their constituents, MPs have to have some idea of how ordinary people live. If you are earning hundreds of thousands of pounds you can't possibly empathise with someone on average pay of £26,000, let alone on minimum wage. MPs' earnings already put them in the top 4 per cent of income earners, so they are hardly being forced to slum it.

Of course, apologists for second jobs say that they give MPs "experience of the real world". But it's curious how this experience always seems to be at the most lucrative end of the real world, on the board of arms companies and as consultants for private firms. MPs don't tend to queue up to gain experience of shelf-stacking in Tescos, working in Citizens Advice Bureaux, or women's refuges.

And the claim that without the prospect of serious money people wouldn't enter politics is contradicted by the obvious fact that the vast majority of MPs do not enter Parliament with the expectation of material gain. There are plenty of people able and willing to do the job. Access to decent child care would improve the quality of MPs, especially women MPs, far more than another pay rise.

What we need in politics are people who are motivated by public service rather than greed; high ideals rather than high salaries; humility rather than vanity; empathy rather than envy. This may seem a tall order, and few of us measure up. But as I say: most MPs in my experience have these qualities. At least to begin with.

Many also have strong egos, but that is no bad thing in a politician. They have to enjoy public exposure and be energised by debate and excited by intellectual combat in a media bubble. Society needs people who are willing to step up to the plate. The task is really to prevent them stepping over the plate once they are up there.

We start by removing temptation - which can corrupt the best of us. That means nudging our politicians in more or less subtle ways to keep on the straight and narrow; and making sure that walking the line is more rewarding than straying from it. In other words, we want our politicians to be Danish

Denmark is the country which always tops the honesty indexes like the one compiled by Transparency International, the global campaign against corruption. Finland, Sweden and New Zealand also score high on the angels list. Countries like Mexico, Malta and Italy are at the bottom. The UK is, well, somewhere in the middle.

But Denmark is invariably cited as the "cleanest" country in the world. In fact, the think tank Sustainable Government says it is the only country where there is simply no corruption. Why? There is maximum disclosure and transparency, vigorous prosecution of wrongdoing; a free and vigilant press; clear rules on remuneration and expenses and a very strong ethic of public service.

Another reason there is so little corruption in Denmark is that there isn't a lot at stake. It is a small country of five million people with a high standard of living but without huge amounts of money flowing through corrupt financial centres. It has relatively high taxes too so bankers and plutocrats tend not to dwell there.

Were Scotland an independent country it would probably score high on the honesty list of clean states. This is because Holyrood has some of the toughest rules on expenses and conflict of interest in the world.

The Scottish Parliament was set up in the wake of the cash-for-questions "sleaze" scandals in Westminster in the 1990s and its rules are designed to make parliamentary payola so risky that no-one would even contemplate it.

Lobbying or "paid advocacy" is forbidden in the Scottish Parliament and neglecting to register earnings is a criminal offence.

The former leader of the Scottish Conservatives, the late David McLetchie, had to resign over wrongly claimed taxi expenses in 2005. MPs in Westminster couldn't believe it. The Labour leader, Wendy Alexander, resigned in 2008 over a donation to a leadership campaign that never actually took place.

And poor old Henry McLeish had to resign as First Minister in 2001 over the sub-letting of his constituency offices before he even entered Holyrood, and even though he was cleared by the Westminster Fees Office. In fact, Holyrood's rules are so strict, you might think that it would deter people from wanting to stand for Parliament, but it doesn't.

The Presiding Officer, Tricia Marwick, has launched a review following last week's scandals in Westminster to see if the Holyrood rules need to be tightened even further. The Scottish Labour leader, Jim Murphy, has called for MSPs to be banned from taking on any paid directorships and any executive positions while serving.

This would hit a couple of members who have farms, family firms or connections with them. But it would mean little to most. One of the higher earners is the SNP MSP, Joan McAlpine, who makes £20,000 a year from a column in the Daily Record.

The rigidity of the rules in Holyrood is one important reason why there has been a succession of Westminster expenses and cash-for-access scandals over the last decade. Nosy journalists have been applying the standards of the Scottish Parliament to Westminster and found it wanting.

The "duck house" expenses scams had been happening for years in Westminster until the investigative journalists Heather Brooke filed Freedom of Information requests to expose them. Neither Jack Straw nor Malcolm Rifkind have probably broken any of the Westminster rules, which are much laxer than here. But they had to resign nevertheless because public opinion simply won't tolerate this kind of behaviour any longer.

My own view is that both Westminster and Holyrood might sensibly introduce the rules on outside earnings that apply in one of the other less corrupt legislatures: the US Congress. Senators and Representatives are only allowed to earn a maximum of 15% of their earnings from outside work. Certain types of earnings - where there is a conflict of interest - are outlawed altogether.

This seems to me to be a fair way of capping moonlighting once and for all. Of course, Congressmen and women earn quite a bit more than MPs: their basic salary is around £110,000. But America is a big country. In the least corrupt legislature in the world, the Danish parliament, MPs are paid the same as MPs in Westminster.

There may be a case for British MPs to earn a bit more in exchange for a capping of outside earnings - but only about 11%. And hey presto - by coincidence, MPs have just awarded themselves precisely that. Next year, the pay of MPs will rise to £74,000 a year - which is good money in anyone's book.

Politicians in Scotland like Nicola Sturgeon or Alex Salmond stand comparison with any ministers in Westminster and they don't complain about their pay. What makes a good politician is firm convictions, a sense of injustice, interest in people, a passion for democracy and a determination to change society for the better.

No, I have to say that I wouldn't pass muster, but I've never been interested in active politics. I'm an observer rather than a participant and I could never fit my belief system into the restrictive container of any particular political party ideology. But I don't apologise. The press is a vital part of the democratic process.

The Sunday Herald's Paul Hutcheon - the man no politician wants to find on the end of the phone - has played a major role in testing the boundaries of parliamentary probity in Holyrood. And, indirectly, in Westminster. Heather Brooke, the journalist who broke open the MPs' expenses scandal in Westminster, used a few tips she gained from Paul Hutcheon on how to use freedom of information requests.

So, the decline in circulation of the press in Scotland - the Sunday Herald excepted - is a major worry. The press is not what it was and it is not yet clear that the internet is capable of holding Parliament to account. Twitter and Facebook don't do this kind of journalism on the whole.

So no-one should believe that somehow Holyrood is immune from corruption. As the Scottish Parliament takes on more spending responsibility, following the Smith reforms, lobbyists and private interests will increasingly target the legislature. PRs and influence-pedlars from big pharma, energy and construction interests are all over Holyrood already, and they have big bucks.

But the voters have a responsibility here too. It was voter apathy and falling turnouts in many of the old Scottish councils which allowed petty corruption to flourish in town halls. PR helped reform them and made voting more relevant to people. A balanced Holyrood parliament with a vigorous opposition and free-thinking MSPs like the late Margo Macdonald, are the best defences against parliamentary corruption.

So there is no great mystery about this. Politicians are not by nature corrupt and very few enter parliament with the express purpose of making lots of money. But they need to be saved form themselves by a robust democracy with transparency, accountability clear rules, sound penalties and an ethos of public service.

It won't bring to an end the spectacle of MPs behaving badly. There are a million ways in which parliaments become corrupted. The revolving door which allows ministers to move into lucrative private sector jobs related to their former ministerial responsibilities is another emerging problem. But cash for access, like cash for questions and cash for duck houses, can and now I think will be addressed.

Last week, MPs in Westminster voted against a Labour motion calling for a ban on all paid consultancies and directorships. But this is now certain to become an election issue and the Tories will have to come up with some alternative that restores public trust. The voters have simply had enough.