It's become a cliche to say that, in 50 years, Britain has gone from Cathy Come Home to Benefits Street. But why has it become so much harder to argue the case for welfare today? Labour's Commons meltdown over the Welfare Bill confirms the extent to which supporters of welfare are on the defensive.

Seven years on from the financial crash, it is the poor who are being made to pay the cost as social protections are withdrawn allegedly to pay down debt. Yet, when income and wealth inequality are at record levels, this must surely seem an injustice to reasonable people.

This is about much more than lack of political leadership: opinion polls such as the British Attitudes Survey indicate that voters in the UK, in Scotland as well as England, are much less supportive of welfare than 25 years ago during the last deep recession.

Tabloid newspapers have intensified the assault on the poor by featuring cases of large unemployed families (often immigrants) receiving huge benefits and living in big houses. But people mostly know from their own experience that these families are very much the exception.

They know this because, unlike in 1990, the vast majority of the poor today are in work. The Joseph Rowntree Foundation says 6.7 million working poor are dependent on tax credits to maintain a basic standard of living. There are far fewer “skivers” today than 25 years ago.

Yet there has still been a breakdown of trust in collective provision. This may partly be to do with large-scale immigration. There is some evidence that people become less supportive of welfare if they believe it is benefitting folk of another culture.

This is most unfortunate because immigrants contribute greatly to the wealth of this country and have played a major role in lifting the UK out of recession. They pay in more in their taxes than they take out in benefits.

But one other important reason why it has become so much more difficult to defend welfare today, and why the Conservatives have been able to push through their reforms with so little opposition, is that in many respects the benefits system we have is indefensible.

No one can really justify a system that taxes middle-income families in order to subsidise companies that pay poverty wages. Yet that is exactly what the tax credits system does, to the tune of £30 billion a year. Six in 10 working families qualify for tax credits.

The answer, of course, is to increase wages. This is what the Tories have done, after a fashion. George Osborne's promise in the Budget of a £9 “living wage” by 2020 was a brilliant, if cynical, exercise in political cross-dressing. Not even the SNP had proposed a £9 minimum wage.

It was cynical because the Chancellor also slashed tax credits for low-income working families. Families earning around £20,000 a year stand to lose more than £1,000 a year.

Thus, an unprecedented assault on the incomes of the poorest “hard working families” in the country was dressed up as a new deal on the living wage. Politics doesn’t get more devious.

Much of the saving on credits will go to wealthy people who are being relieved of death duties on million-pound houses and to pay for higher income-tax thresholds for those earning up to £50,000.

The Conservatives always look after their own: the middle class home owners of suburbia, though, rarely have they been so blatant about it. It is the failure of the opposition parties, academics and non-government poverty agencies to come up with an alternative that is the real problem.

Endemic low pay also has a lot to do with the decline and fall of the trades unions which, outside the public sector, have become a marginal force in Britain. With the ending of collective bargaining, the income playing field has been tilted significantly in favour of capital and against labour.

The benefits cap in 2012 was another astute move by the Tories who realised that, to most people, £26,000 a year seemed more than fair. Most working people earn less than that sum, so why should workless families receive more courtesy of the taxpayer? The cap was, and is, supported by a majority of voters in Scotland.

But, as I argued at the time, this was only a first step. The cap has been reduced to £20,000 (£23,000 in London) and the Welfare Reform Bill will allow future chancellors to reduce it further without legislation.

This was a classic exercise in salami slicing. But the result could be catastrophic for social cohesion. Reducing the cap progressively amounts to a form of social cleansing. Lower income families will be forced out of the south-east of England where rents are already more than £1,200 a month and unaffordable for the low paid.

The proposal to cut benefits for third and subsequent children is also widely supported by many voters. If they can't afford more than two children, why should the welfare claimants and immigrants be given the means so to do out of their taxes?

Universal child tax credit is a difficult thing to justify and, again, Labour were unable to mount the case for it; which is, of course, that the state shouldn't penalise children for the circumstances of their birth.

Scottish politicians have railed against these changes, rightly. But they may be fashioning a noose for themselves. The Conservatives are saying: well, if you don't like these measures you can put up income tax in Scotland to pay for higher benefits.

This is a fiscal trap because it will be very hard to pay for higher benefits through income tax in Scotland without robbing Peter to pay Paul. Scotland's income tax base is shrinking relative to England's because of out-migration and Holryood's lack of economic powers to promote growth.

Nor will the Scottish Parliament have powers to vary other revenue streams such as national insurance, VAT, excise duties or hydrocarbon taxes. This is no accident; it is hard politics. The Tories hope it will destroy the SNP’s astonishing popularity, and well it might.

The Scottish budget will be further squeezed by the Chancellor's latest proposal for a further £40bn in spending cuts which will reduce Scottish spending through the Barnett Formula, or its successor, by £1bn.

But these are complex arguments. As with the benefits cap the Conservatives' income tax devolution is as simple as it is disingenuous.

Combined with the benefits cap, a picture emerges of fiscal gerrymandering, with communities in the north of England and in Scotland required to support an increased number of dependent families while the wealthy are shielded from taxation in a south-east fortress where income tax increases are to be outlawed.

We are seeing a new socio-economic geography emerging in Britain, the very antithesis of one nation. This is not a Britain many would want to live in. Indeed, there is some evidence from recent YouGov polls that people think the Conservatives may have gone too far.

Without serious opposition in Parliament, nothing is going to stop the most single-minded, class-biased administration since Margaret Thatcher's in its determination to push the poor out of sight and out of mind.