London Briefing: If one of the key features of fascism is the ability to make trains run on time then nobody could accuse the current government of fascist tendencies. As public expenditure continues to explode, the public infrastructure continues to decay.

Safety concerns have been raised, yet again, on the London Underground following two deeply worrying derailments. If the Northern Line faces partial closure the cost of the ensuing chaos will be incalculable. Yet again, we see evidence of the key problem facing Tony Blair: rising spending and taxation is not leading to perceptions of improved public sector services.

Ministers will undoubtedly say this is unfair. Some data is beginning to emerge that suggests some of the extra cash is beginning to show up in improved provision and not just in public sector pay. But you really do have to look hard to find these gains; they are far from obvious to the average voter.

It might also be argued that it is still too early to expect much visibility, given the clear lags between making the investment and the eventual outcome. The Tube is a case in point and is a particular example of something called a Public Private Partnership (PPP) which, as the name suggests, is an attempt to blend the best of both worlds.

The particular "partnership" involving the London Underground and the private sector has only just got going after years of argument. It will be many more years before we are in a position to judge the success or failure of the project.

As a matter of fact, PPP also (enthusiastically) embraces something called the Private Finance Initiative (PFI), a notion dreamed up by the last Conservative government in 1992. PFI essentially involves contractors taking on the costs of building, say, a hospital, school or prison. The private company makes its money by renting the finished building or road back to the government or local authority.

PPP sounds an excellent idea. It appeals to Tony Blair because it potentially involves the participation of the private sector in many areas of the public sector, areas that are clearly marked "not for privatisation".

Unions, of course, hate it. Health is the obvious example: the NHS cannot be privatised, is falling apart and few people believe that the extra money being spent on it is making a difference. And yet, possibly the biggest hospital building programme ever is currently under way, thanks in part to PFI. At least six major projects have already been finished, 17 hospitals and other key facilities are being built and there are plans for a further 45.

At least eight new prisons have been built under PFI with lots more to come. Important road schemes are also under way. Of course, it has not all been plain sailing and there have been some spectacular failures.

Unfairly, perhaps, the failure of Railtrack has given the whole privatisation process, not just PPP a very bad name. But it is just possible that critics of PPP, including this columnist, by concentrating on the obvious weaknesses have missed some of the successes. And those successes may become more visible over the next few years.

None of these issues are unique to the UK of course. Anybody who argues that private sector provision can improve on the public sector's performance is immediately faced with a political backlash.

PPP is a classic political compromise, one that is being tried in other countries as well. It is, perhaps, a modern version of the old "mixed economy" model. Politicians of both left and right like PPP. It represents a pragmatic recognition that, generally, the private sector is much more efficient and gets things done that, for all sorts of reasons, the public sector seems chronically ill-suited to achieve.

But it stops short of full privatisation and the political war that would inevitably follow. Ideologues of all persuasions hate PPP because it is a compromise: it is neither a wholly free-market solution nor pure state-owned enterprise.

It would be surprising if some of the money being thrown at the public sector - either directly or via PPP - doesn't show up somewhere in improved services. Never underestimate the power of large sums of cash.

PPP represents a key part of a much larger experiment. I have always been concerned that political compromises rarely offer economically literate solutions. Unusually, PPP does not offer politicians instant gratification; over the next couple of years we will find out if it offers any returns at all.