I took a stroll through the heartlands of British Government the other evening, and very affecting it was too.

I ambled down Horseguards Road from Trafalgar Square past the tradesman’s entrance to No.10 (presumably there will be a few more cases of Scotch whisky being delivered there soon, unless the monumentally dour Brown does not drink); did a U-turn back up into Whitehall (unthinkable for a certain Mrs M Thatcher); then cut down Horseguards Avenue towards the Embankment, with the giant bicycle wheel of the London Eye turning its panoramic circles for the tourists dead ahead.

Along the way I passed the Foreign Office, the Treasury, bits of the Ministry of Defence, and various buildings just vaguely known as ‘Government offices’ (perhaps the Ministry for Silly Walks is located in one of these). I did not see Her Majesty’s Revenue and Customs (HMRC) offices, but I know they are tucked away there somewhere, nearer the Houses of Parliament I think – but you can’t get a Government office’s postal address off the Internet for love nor money these days.

Anyway, if you take this stroll for yourself you cannot fail to be impressed by the sheer massiveness of the buildings and the majesty of the apartments of the State. The architecture is from the height of Britain’s imperial dominance of more than a third of the globe – solid, huge and fortress-like in many ways. And it’s sobering to think that some of the brightest minds in the country – if not the world – work in these imposing piles. They may not be the quickest, say, compared to the City whizz-kids (civil servants think an urgent deadline means sometime this decade), but I bet there are more Double Firsts in Classics from Oxbridge per square metre of office space there than anywhere else on the planet.

In a way you’d be forgiven for thinking that the tax you pay would be spent wisely by these cerebral sages, oiling the machinery of good governance and ensuring that the nation’s body politic remains in a state of Marathon-ready fitness – lean, energy-efficient and conducting best-practice economic ergonomics on behalf of the electorate.

In a way you might think that – but something is rotten in the State apartments housing HMRC and the material that’s giving off the evil pong is the tax credits pile that sits festering in the less salubrious reaches of the legislative garden that is Whitehall.

This initiative, launched to a public that had done nothing to deserve it in 2003, has been an unmitigated disaster from the start, the prey of criminals and conmen and the terminally bewildered (including HMRC staff) who cannot fathom its labyrinthine rule structure. We learn today, without the least start of surprise, that “another £1.4bn” is to be written off in overpaid tax credits, although HMRC feebly protests that overpayments have fallen by a fifth in the tax years 2003-04 and 2004-05.

Big deal. Edward Leigh, chairman of the committee of MPs poking around in the rubble of tax credits, thunders thus: “Billions of pounds, far more than those who thought up the system ever envisaged, are still routinely overpaid to claimants. Very large amounts have to be written off. And the attempts to recover overpayments from genuine claimants have caused significant suffering to many vulnerable families. HMRC seems incapable of mounting a credible and effective response to the flood of money being wasted in this way.”

Quite so – and don’t forget that this is your money being squandered. I trust someone skulking around in one of those massive buildings in Whitehall is suitably ashamed of themselves and steers clear of dreaming up any more lamentable initiatives in the future.