The FT has reported that Nick Clegg, the UK Lib Dem leader has said that:

Lib Dems have abandoned their plans for a 50 per cent top rate of income tax for high earners, but that the 40 per cent top rate should mean 40 per cent

That's an idea from the Missing Billions.

The idea is simple, but effective. We know that people do not pay tax at 40% in the UK. Allowances and reliefs ensure that is the case. As I showed in the Missing Billions, reliefs costing some £8 billion a year go to those earning more than £100,000 a year: they are the wealthy in this country representing about 1% of the population of taxpayers.

If they were required to pay a minimum tax rate (and I stress, I quote examples) of say 32% on £100,000 of income, 36% on £150,000 of income and 40% on £200,000 of income vast ranges of loopholes would disappear, the complexity of the tax system (created mainly for the benefit of this group) would fall dramatically and the tax system would be progressive but with a still modest top rate, which most assume they might pay now, but don't.

It's a simple change: the ramifications are significant.