Father Timothy Russ also said that Mr Blair, an Anglican, “may well” convert to Catholicism. The revelation will increase speculation that Mr Blair is preparing to convert to Roman Catholicism despite a clear denial from Downing Street.

Father Russ is invited regularly by Mr Blair to say Mass in a drawing room at Chequers, the Prime Minister’s weekend retreat. A table is used as an altar.

The services are attended by the Prime Minister, his family and house guests. Mr Blair used to attend Father Russ’s parish church of the Immaculate Heart of Mary in the nearby village, but for security reasons rarely does so now.

Mr Blair’s interest in the Church is growing and he has told Father Russ: “Theology is much more interesting than politics.” He has also asked him whether the Prime Minister of Britain could be a Catholic.

If Mr Blair converted while in office, he would be the country’s first Catholic Prime Minister, although there is no constitutional bar to a Catholic in Downing Street.

Cardinal Basil Hume, the late Roman Catholic Archbishop of Westminster, wrote to Mr Blair in 1996 demanding that he cease taking Communion at his wife’s church in Islington, saying that it was “all right to do so when in Tuscany for the holidays . . . as there was no Anglican church near by.”

Mr Blair promised to stop receiving Communion at the Church of St Joan of Arc if his presence there caused a problem for the Catholic authorities. But he made clear that he did not agree with the decision in a pointed letter to Cardinal Hume which said: “I wonder what Jesus would have made of it”.

The Pope issued an encyclical last year which said that Communion could be given to an Anglican only if it was required to “ meet a grave spiritual need for . . . eternal salvation”. Earlier this year, Mr Blair, whose wife Cherie is a Catholic, took his first Catholic Communion in public for seven years when staying in Cusona, Italy, offending local clergy and leading to demands for an investigation by the Vatican.

However, Father Russ, parish priest in Great Missenden, yesterday insisted that Mr Blair could receive Catholic Communion.

He declined to confirm that the Prime Minister was taking Communion but defended the use of the principle of epikeia, which allows exceptions to rules under certain circumstances, in such situations.

He said that it would be “unwise” to speculate that the Prime Minister was close to converting. “It might well end up that way but a lot of things would have to change in his modus operandi and in his way of thinking and working before he could be a Catholic.”

The epikeia principle, outlined in Canon 1752, allows priests to override the strict letter of the law in cases where rigid application of the law would frustrate the intentions of the author, or God. The Canon states that the salvation of souls in the Church must always be the supreme law.

Sources close to the Archbishop of Westminster, Cardinal Cormac Murphy-O’Connor, indicated that under the epikeia principle, there would be no objection if Mr Blair had been receiving Communion. Father Russ said that he was concerned about the Prime Minister’s views of the moral order and the sanctity of family life.

He said: “Tony Blair is a lazy thinker when it comes to certain ethical questions.” But he said that the Catholic Church fulfilled many of the Prime Minister’s socialist ideals.

Downing Street said last night that Mr Blair had no plans to convert.

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