The photographs are said to show the minister - who has not been named - embracing a younger person, who could be a teenager.

Ann Widdecombe said the affair was evidence that Prime Minister Tony Blair is losing control of his ministers.

Widdecombe: "They have packed in more sleaze in 18 months than we did in 18 years"

Speaking on GMTV's The Sunday Programme, she said: "This is the Tony Blair who before the last election said they were going to be whiter than white, purer than pure but they have packed in more sleaze in 18 months than we did in 18 years.

"And now we have got these fresh allegations the truth of which I cannot possibly determine.

"It is a childish display because of a clash of personalities in the Labour Party and Britain is suffering from it.

"Tony Blair gives the impression of being a man who talks tough but he is very much out of control of his own party."

'No plans to publish'

Mr Robinson has told friends he has the pictures in an attempt to stop allies of the prime minister leaning on him to water down his memoirs, according to The Sunday Times.

It says Mr Robinson has no plans to publish the pictures.

But the paper says his friends want to make it clear that Downing Street should be grateful that his imminent autobiography, The Unconventional Minister, will not prove as difficult for the government as it could have done.

One person who has seen the pictures is quoted by the paper as saying: "They are not explicit in the usual sense of the word but it is pretty clear what is going on.

"It is obvious they are more than friends. They are not the sort of pictures you would want to be made public."

Speculation

The content of Mr Robinson's memoirs has caused much speculation.

It has been said that the book will detail money which Mr Robinson gave to Mr Blair's "blind trust", which paid for his office costs when Labour was in opposition.

But earlier this week, the trustees took the unusual step of releasing a statement saying Mr Robinson had never donated any money to the fund.

It has also been reported that the prime minister's press secretary, Alastair Campbell, solicited funds for the Labour Party from Mr Robinson. This has also been denied.

Mr Robinson was forced to resign as paymaster general last December after it emerged he had secretly lent Peter Mandelson £373,000 to buy a house in Notting Hill.

It is said he is angry that Mr Mandelson has returned to the Cabinet while he is still on the backbenches.

A Downing Street spokesman said: "Given that so much speculation about this book has already proved to be wide of the mark we have no comment to make whatsoever."