It's set to be the second largest legislature in the world after the Chinese Politburo with nearly 900 members. It debates and votes on the laws of the land. It costs the public purse tens of millions of pounds each year. And it is elected by nobody.

I refer, of course, to the UK House of Lords, the biggest parliamentary abomination in any Western democracy. Indeed, it is hard to call the UK a democracy when it allows unelected peers, through accident of birth or patronage, to decide its laws.

The disgraced former Deputy Speaker of the Lords, Lord Sewel, may have made the case for reform even more urgent now that we know how some of its members spend their down time. He said many do “f*** all” for their £300 daily allowance.

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But David Cameron has answered the clamour for reform by brazenly announcing another 50 new unelected Lords. Thirty five are Conservative peers, and they will be there to boost the Tory majority in the Upper House. It is an insult to every voter in Britain.

Parliamentarians in the USA, Canada, and Australia, find our system utterly incomprehensible. How can we be a democracy when we allow a prime minister to create members of parliament by the stroke of a pen, thus rewarding former ministers, party donors and toadies alike. It is breathtaking in its absurdity and an invitation to corruption.

The Lords has a key legislative role. There may be a convention that it does not overturn bills that were foreshadowed in a governing party's manifesto. And since the 1911 Parliament Act, when the Lords tried to block the creation of the original Liberal welfare state, the Lords cannot overturn a money bill.

But it does still have a profound impact on legislation, especially on the constitution, and can hold up and frustrate legislation by repeatedly rejecting it. It may be instrumental, indeed, in frustrating the Government's plans for English Votes for English Laws (Evel) on the grounds that it is a constitutional innovation almost as absurd as the Lords itself.

There is, of course, a place for a revising chamber: a legislature elected on a different franchise that can oversee and reflect on partisan or ill-thought-out bills such as Evel emanating from the main legislature.

Indeed, the former Presiding Officer of the Holyrood Parliament, Lord Steel, has said that one of Holyrood's problems is the lack of an upper house that can take a second look at daft measures on matters such as offensive behaviour at football matches or the abolition of corroboration in criminal trials.

However, the revising chamber does not need to be filled with the scions of superannuated aristocrats, mega-rich party supporters or government placemen and place-women. In many democracies such as the United States, the "upper house" is a senate with members elected on a regional basis.

Many have argued for this to happen here as part of a federal restructuring of the UK. But the Prime Minister's answer to this has been clear. He has said that Lords reform is a waste of time and that he's jolly well going to fill it with more of the same. So you'll have had your federalism.

Now, the SNP has boycotted the House of Lords on the grounds that no democratic party should participate in an anachronistic relic of feudalism. This is understandable but I'm not entirely sure that this boycott makes sense any more. There needs to be a proper debate about this. The game has changed.

As the third party in the House of Commons, the SNP could be in line for a significant number of seats in the Lords under the obscure conventions that govern these things. We have seen how influential they can be in the Commons; they need to take this energy into the very heart of the UK Establishment. They should be in there exposing what goes on to public view.

However, whenever you suggest this, SNP people on social media cry out. Hypocrisy! Jobs for the boys! Sell out! I'm told that the SNP would be a laughing stock if they abandoned their principled stand and sat in the coke-snorting, champagne-quaffing, expenses-fiddling House of Sin.

But I'm not sure exactly where the hypocrisy lies. And who exactly is going to accuse them? Certainly not the Labour or the Liberal Democrats or even Plaid Cymru. If the Green Party can send representatives to the Lords, as it does, I don't see why the SNP can't.

You either participate in the UK parliamentary system or your don't. Sinn Fein decided to withdraw from Westminster altogether in 1918 after their “tsunami” election on the grounds that it did not recognise Westminster's legitimacy to rule in Ireland. That is a principled stand.

The SNP decided otherwise. It is participating in Westminster, so it seems pointless to boycott one part of it. Their MPs have sworn an oath to the Queen, for heaven's sake, and you don't get much more establishment cop-out than that.

There is indeed an argument that the SNP owe a duty to Scottish voters to fully represent them throughout the UK houses of parliament. The House of Lords is as much a part of the UK Parliament as the select committee system or cross-party parliamentary groups.

There is a raft of measures hitting the Lords – devolution, human rights act, Evel and so on – in which Scots have a direct interest. For obscure reasons, it is often actually easier to amend legislation in the Lords than in the Commons. I just don't see the logic in silencing Scotland's voice.

Participation doesn't mean capitulation, or tacit acceptance of the unelected principle. The SNP could agree to sit in the Lords only as Abolition Peers. They should call on the other parties to do the same, especially Labour. They flunked Lords reform when in government.

The intention would be to gradually fill the Lords with explicit abolitionists who remain there only on sufferance. The minimal case for membership of the Abolition Lords would be for a constitutional convention on the future of the unelected Lords and a commitment to elected peers. In time, it might be a majority.

Anyway, I have never heard the Lords boycott discussed within the SNP, and now is the time. The Nationalists are abandoning a lot of their old conventions, such as not voting on English legislation. Seeking influence in the Lords makes more sense than voting on fox hunting.

Perhaps the SNP are worried that their Lords might "go native" and turn into substance-abusing debauchees; or that they might become addicted to expense-account living. Many Lords make a pretty penny as lobbyists and hired hands for private interests.

But the risk of going native is arguably greater in the Commons. Any SNP Lords would be under intense scrutiny for their personal integrity anyway. So what are they afraid of?

The case for reform of the Lords needs to be taken into the Lords itself. If democrats just walk away they assist it in its role as a bastion of unelected privilege. By boycotting the Lords, the SNP are doing the Establishment's work for them.