But I think we can agree some terms, can’t we? To be “progressive” tax changes need to do more in distributional terms for the relatively less well-off and are “regressive” if they do the opposite primarily benefit the relatively affluent. And an important test of the overall approach of the progressive parties (Labour, LibDem, Green) and of any other parties aspiring/claiming to be progressive is that their changes make the tax system overall more progressive, rather than more regressive.

These aren’t the only considerations in making policy, but this matters – and it can be factually determined, analysed and referred by the IFS,ec.

This is also one important fairness test of individual proposals from all of the parties. Eg, Labour’s 10p tax abolition was regressive. the Tory inheritance tax proposal and the marriage tax break are clearly regressive in their distributional consequences. Other arguments of fairness or merit can be made for them, though the marriage change offends other fairness instincts in discriminating against widowers, and in favour of John Terry, etc. And clearly nobody can or will abolish VAT, but its regressive feature is worth bearing in mind in terms of whether it would be the right tax to raise, etc.

There may then be other considerations – such as those of convenience, stress, how it feels to be in one type of system rather than another (eg stigmatising/non-stigmatising issues around means-testing/universalism). These will be important, though can be less tangible and more contestable, and we can debate how far we would trade them off against distributional fairness. (EG, we have warned against a purely needs-based targetting which is too narrow, on grounds of stigma and non-sustainability over time, but that is to lock-in distributional fairness in the long-run).

But the distributional analysis of tax changes is not theoretical but surely central to a progressive analysis, though you might want to add other considerations to it. When John Kampfner and others argue the LibDems have the most redistributionist platform, he must surely mean that in this distributional sense. He can not be relying only on non-financial elements of the tax changes, without stretching or losing any meaning of what redistribution means.