Another Tory boy for David and Samantha Cameron

David Cameron became the father of a 7lb 3oz boy yesterday. His wife, Samantha, gave birth to their third child by Caesarean section at St Mary's Hospital, Paddington. The baby's name has not yet been announced. The Tory leader, who rushed to his wife's side for the birth, announced afterwards: "Everything is fantastic, it's really exciting."

Speaking outside the hospital, Mr Cameron added: "He's lovely, he has blue eyes and black curly hair. It was all over very quickly. Everything seemed fine. Sam is doing really well, she's sitting up and will be here for a couple of days."

The Camerons have a severely disabled son, Ivan, born in 2002, and a daughter, Nancy, aged two.

The Tory leader will now take two weeks' paternity leave. The shadow Foreign Secretary, William Hague, will stand in for him today at Prime Minister's Questions, pitting him against Tony Blair for the first time since he stood down from the Tory leadership in 2001.

The Prime Minister's office said Mr Blair would congratulate Mr Cameron "in the appropriate way at the appropriate time".

The shadow Health Secretary, Andrew Lansley, jubilantly told MPs the Valentine's Day addition to the Cameron family was just one of four children fathered by Tory MPs in quick succession. The partners of Adam Afriyie and Greg Hands, the Tory MPs, respectively, for Windsor and Hammersmith and Fulham, have recently given birth, and the MP for Monmouth, David Davies, is due to become a father soon.

"We on this side are doing our bit to defuse the demographic time bomb," Mr Lansley joked.

Until recently, it was unusual for major party leaders to become parents in office, since most were of an age when their children were growing up. But Tony Blair led the way with the birth of Leo Blair in 2000.

Charles Kennedy became a father during last year's general election campaign. The next political birth is scheduled in July, for Sarah Brown, the wife of the Chancellor.

Yesterday, Mrs Brown launched a campaign against domestic violence, for the charity Women's Aid. Mrs Brown, who is involved with a number of charities, said: "Domestic violence remains a taboo issue for many and we hope to get everyone, not just those in violent relationships, to think and talk about the reality for hundreds of thousands of women every year."

The campaign includes posters related to Valentine's Day. One has a single red rose and the caption: "Suzy, I told you to shut up, you stupid cow. It's your fault I hurt you. Pete."