Tony and Cherie Blair have turned down the chance to find out which sex their fourth child will be, the Prime Minister has revealed.

Mr Blair disclosed that his wife had recently had a scan during which she was offered the opportunity to find out the baby's sex, but they declined the offer.

He said the moment Cherie told him that, aged 45, she was pregnant was "very memorable."

In his first interview of the century, Mr Blair told Breakfast With Frost: "It was wholly unexpected. I'm 46 and she's 45 - it's not quite what you expect.

"On the other hand, it's a wonderful thing. What is amazing to me is how many people I now meet who have had children later in life.

"I'm constantly having people coming up to me."

Changing nappies

Asked whether he wanted to find out whether it was a boy or a girl, Mr Blair said: "Well, we had that chance when we had a recent scan but we decided not to."

The Blairs were considering "some ideas" for names, he added.

Sir David suggested that he might consider the name Ken if the baby is a boy - a reference to Labour MP Ken Livingstone, one of the London mayoral hopefuls and a thorn in Tony Blair's side.

Mr Blair grinned before replying: "It's a possibility."

Reflecting on the new baby's arrival this summer, Mr Blair said: "It will make a difference, but on the other hand, it's not so long ago that I can't remember (bringing up children).

"I'm really now looking forward to it. It's just at the time I got quite a shock."

Asked whether he would still be "up" for changing nappies in the middle of the night, Mr Blair said: "Yes ... I'll do that again."