The blame, of course, was placed firmly on the shoulders of new Labour, which from this term, abolished the Oratory’s cherished grant-maintained status.

But checking on the detail of its well-publicised claims is difficult. The Oratory - a top-performing school which counts the Prime Minister’s sons among its 1,350 pupils - has failed to publish accounts for at least four years.

Its books are available at the school for inspection. But there is no information on the way the school has spent its pound;4.5 million budget in the governors’ annual reports - a clear breach of the law.

The Department of Education and Employment has confirmed it will be demanding an explanation for this omission. The school’s next annual report is expected to include spending details.

Even without the accounts it is evident that the school took advantage of its GM status to fund a style of education which would be the envy of most state headteachers.

In his letter to parents last week, which asked for pound;30 monthly covenants, headteacher John McIntosh listed some of the advantages:

an arts centre, with 340-seat theatre;

a new chapel;

staff paid above national rates;

a new pound;1.2 million roof:

a specialist music junior school.

The school says its choir provides a “rigorous choral education” for Catholic boys, of a kind “hitherto only available in the independent sector”.

Such things have not come cheap. Last year Hammersmith’s Sacred Heart high school, where Mr Blair’s daughter is a pupil, received pound;2,544 per head. Pupils at the Oratory had pound;3,323. Yet 21.6 per cent of Sacred Heart pupils were entitled to free school meals last year, compared to just 8.5 per cent at the Oratory.

This year the funding of the two aided schools is much closer with the Oratory getting more than pound;300 less per pupil.

“We are just not getting the grant we have been getting,” says Mr McIntosh, who is credited with helping to devise GM status when Kenneth Baker was the Conservative Education Secretary.

But others suggest the Oratory and other GM schools failed to plan ahead. Labour came to power committed to abolishing the sector. The Tory government had already started reining in GM spending following attacks on “double funding” by parliamentary watchdogs - many GM schools received money for the same services from both local and central government.

The Oratory was the biggest beneficiary, receiving an additional pound;503,566 between 199495 and 199899. Several others received between pound;300,000 and pound;500,000.

Martin Rogers, of Education Network, a research and information centre funded by education authorities, said: “In 1995, the Oratory and other GM schools had five years’ notice of a reduction in their budgets. If they didn’t take appropriate action, it is not surprising they have got problems now.”

But Mr McIntosh insists that his budget problems only emerged this year, and that it is not possible to point to one issue - such as higher teacher salaries - as a cause of its difficulties. The Oratory is one of the few schools to have opted out of the national pay scales.

He said: “The funding has changed for (formerly) GM schools and there has been no increase for inflation for three years. There are a lot of GM schools in the same position as we are.

“The school has had a level of funding that enabled it to recruit high-calibre staff. We and the parents would like to retain that. ”

Mr McIntosh denied the timing of the letter to parents had anything to do with this week’s Labour conference. He said he and the governors had been discussing funding issues throughout the summer, and that the letter was issued after a governors meeting on September 16.

“I was not aware the party conference was coming up. It’s not my scene,” he said.

Mr McIntosh said this week that the school’s local authority, Hammersmith and Fulham, had offered the governors a three-year deficit facility to help cover the pound;250,000 shortfall.

The letter is available on the Oratory’s website www.london-oratory.org