The prime minister's wife, Cherie Blair, has discovered she has a 35-year-old half-sister she never knew about.

The Daily Mail claims Lucy Thomas was born after a brief relationship between Mrs Blair's father, the actor Tony Booth, and a radio sales girl, Ann Gannon.

But Downing Street has declined to comment, saying it was "an entirely private affair".

Mrs Thomas, 35, who now lives in Australia, told the Mail that she had spoken by telephone to Mrs Blair and that they were hoping to meet later this year.

Booth in a scene from Till Death Us Do Part

"I'd like to think that in the conversations we've had we've made some kind of connection. I'm very happy that I'll be meeting her soon," she told the paper.

Mrs Thomas, who is married with a six-year-old son and works for a television company in Sydney, declined to say how she first came to contact Mrs Blair.

She did disclose, however, that she first spoke to Mrs Blair by telephone when the Prime Minister and his wife were in Australia in March for the Commonwealth Heads of Government Conference at Coolum, near Brisbane.

Mrs Thomas told the Mail she was now looking forward to meeting Mrs Blair and her six other sisters.

'Excited'

"The reception from them so far has been wonderful. They've been very welcoming," she told the paper.

"I have no expectations that would put any pressure on any of us but I am excited and my son Peter can't wait to meet them all."

She said she had been watching Mrs Blair's career closely and was "very impressed by Cherie's achievements".

An undisclosed Downing Street source is said to have told the Mail Mrs Blair was "delighted" to have found her half sister and was looking forward to a face-to-face meeting.

Mr Booth, an actor, is best known for his part in 1960s television series Till Death Us Do Part as Alf Garnett's son-in-law Mike.