London Briefing: Chancellor of the Exchequer Mr Gordon Brown's latest review of public spending plans contained little that had not been previously announced, yet it attracted huge media coverage. Like the budget statement, the more infrequent reviews of government expenditure elicit much speculation but deliver little that excites.

Gone are the days when stockbroker economists would stay up all night analysing the Chancellor's words.

Much of the media took the line adopted by the rising star of the Conservative party, finance spokesman Mr Oliver Letwin, and attacked the Chancellor for promising yet more spending increases.

Mr Brown reckons he can finance higher expenditure without raising taxes - something that depends entirely on the UK economy continuing to grow reasonably strongly. Any economic downturn, whether the Chancellor's fault or not, will cause borrowing to explode.

The government will then be faced with a difficult decision: raise taxes (and make the downturn worse) or scrap its long-term fiscal rules.

This will be more significant than usual given the UK's current occupation of the fiscal moral high ground: Europe's destruction of its own Stability and Growth Pact has allowed Mr Brown to become holier than thou when dealing with his euro-zone colleagues.

The massive growth already seen in spending on education and the health service is beginning to have an impact but there is still enormous doubt over whether or not we are getting anything like value for money. Spending in these key areas is set to grow further to 2007 - much faster than the growth in the economy.

Peering through the statistical fog is difficult, if not impossible, but the emerging message appears to be that public spending is up a lot but the output of the public sector is only up a bit. Hence, the Tories are arguing that they can cut spending without impacting on services by simply reversing Mr Brown's wasteful increases.

This "symmetry" argument assumes that it is easy to reverse a spending rise that simply involved the hiring of a pointless bureaucrat or increased public sector pay without any commensurate rise in the output of the government sector. History teaches us that it is infinitely easier to raise spending than it is to cut it, no matter how wasteful the original increase. Having created a huge amount of waste, Mr Brown is now trying to take the credit for its elimination over the next four years.

Spurious precision has always been one of Mr Browns' more irritating affectations but he has committed to eliminating 84,150 civil service jobs. Most commentators think that he has no chance of delivering this objective: the public sector is still on a hiring binge and the unions are stirring themselves to have a quiet word in Mr Brown's ear.

In promising a big efficiency drive, Mr Brown is probably just trying to take the wind out of the Conservative's sails and has few intentions of firing the people he has only recently hired.

The Conservatives have an interesting and simple theory about the relationship between the size of the public sector and the health of the overall economy. They believe there is a kind of "tipping point" that marks the maximum size of the public sector. If government gets any bigger than this, the health of the whole economy is damaged.

Evidence for this proposition usually falls under the heading "Europe" but it is not yet a widely accepted idea in mainstream economic thinking. Mr Brown does, however, seem willing - whether wittingly or not - to provide a real-world test of this idea.

Having cut the size of government during the Thatcher years, the Tories now seem to think that the final legacy of that period is about to be squandered. Mr Brown's resurrection of big government has now taken us past the tipping point once again and, on the Tories line of reasoning, the long boom will now inevitably come to an end.

Time will tell of course, and even if Mr Letwin is right, any damage to the structure of the UK economy caused by Mr Brown's great experiment is unlikely to come in time for the Conservatives to reap any benefits this side of the general election. Despite New Labour's woes at the hands of the electorate at the recent by-elections, the Tories are finding it impossible to present themselves as a serious alternative government.

Mr Brown's spending review should be seen as a nakedly political exercise, designed to head off the most potent threat posed by the Conservatives.

Now that Mr Brown is taking care of all of the self-inflicted waste, we can all stop fretting about future tax rises. That is the message we will hear again and again in the run up to the general election, now probably only nine or 10 months away: last week's by-elections revealed an unpopular government but one that will remain in power thanks to the simple fact that the Tories don't have enough stars like Mr Letwin.