The annual report on the Tube public-private partnership should send a shiver down the collective spine of Londoners returning to their desks after the summer break.

London Underground managing director Richard Parry comes as close as he presumably dares to warning the capital that despite all the additional weekend closures granted for the Jubilee line re-signalling project, it may still not be finished by the end of the year.

In surprisingly bald language, the report states: "A failure to deliver the Jubilee line upgrade on time would not only try Londoners' patience even further but would also impact on the upgrades that follow." Tube Lines' progress has been mich slower than anticipated. LU is deliberately putting pressure on the company and, in particular, its shareholder Bechtel.

There is another, even bleaker, assault on the other, now-dead, PPP company: "The legacy left by Metronet's former shareholders was one of poor programme management and system integration, ineffective cost control, a lack of forward planning and inefficient fiscal management."

The report suggests that now the Metronet work has been brought back in house, control has been re-asserted.

It is hard to believe that Gordon Brown was such an enthusiastic cheerleader for the PPP and for the companies that signed up to do the work. Not since the poll tax can a government policy have been such a well-predicted and conspicuous disaster.

The National Audit Office estimated the cost of the failure to the taxpayer was between £170million and £410million, though LU says the final figure will be higher.

Passenger numbers are down four per cent in 2009-10. Fare income will fall below targets. LU is struggling to agree costs with Tube Lines for the second 7½-year period of the PPP. The so-called PPP Arbiter is likely to have to decide what finally happens. It is inevitable some improvements will be delayed or abandoned.

After 6½ years of work and close to £10billion of investment, it is still impossible for Londoners to judge whether the vast sums spent on the Underground represent anything like value for money.

Metronet, responsible for two-thirds of the work, went bankrupt. The remaining company, Tube Lines, is approaching judgment day as completion of Jubilee line upgrades approaches.

One thing is for sure, the Treasury must rue the day it ever allowed itself to be convinced the PPP was a good idea.

Tony Travers is director of the LSE's Greater London group.