Flat tax. The only system that does what it says on the tin

George Osborne, one of the few Conservative MPs who doesn't want to be leader - and the first to say so - is publicly toying with the fashionable notion of a "flat tax".

This matters because Mr Osborne's lack of ambition stems from his enthusiasm for remaining his party's shadow Chancellor.

Unless his new leader, whoever that may be, sacks him, it will fall to Mr Osborne to attempt what his predecessors failed to do in three General Elections - devise a plausible alternative to Gordon Brown's blatant slide back to Old Labour tax and spend.

Flat tax has the political virtue of being different, successful in countries that have tried it and the only tax system in the world that does precisely what it says on the tin.

All taxpayers pay the same, merciful, percentage of their income above an initial taxfree allowance without any ifs, buts, or dodges. That is the theory.

The practice is that the countries where flat taxes have worked are former Communist states - starting with Estonia emerging from the Soviet Union - where there was no effective mechanism for collecting taxes and no array of exceptions and legal loopholes to reward taxpayers whose financial behaviour is favoured by the Government.

That is the British way, starting with pension contributions. Amid all the competing ideas for sorting out the great pensions crisis, everybody takes it for granted that contributions will stay taxfree. Gordon Brown is blamed, rightly, for unleashing much of the present havoc by taxing pension funds' dividends.

Scrapping tax relief on contributions would be worse, wrecking any new pensions structure erected in the life of the present Government.

Then are we sure we want to pay tax on whatever we give to charities? The charities would be dismayed. Yet once you get two loopholes, there will soon be three, four and 17. The tax will cease to be either flat or merciful.

Anyway what about Mr Brown's favourite tax, National Insurance? Does it get swallowed up in the flat rate? If so the rate would be too high for Conservatives' comfort. The Estonians shunned this.

Instead they have a separate and hefty social security levy paid entirely by employers. But it is still part of their payroll cost that would otherwise be available for pay and perks.

Mr Osborne knows all this. He is airing the idea without committing himself to it, setting up a "commission" to beaver away until the next General Election starts to loom. If something ever comes of it, we'll have a shock.