WENDY Alexander yesterday took charge of her latest portfolio - motherhood.

The Labour member for Paisley North gave birth to Valentine's Day twins at the Princess Royal Hospital in Glasgow, her family announced. The delivery, at 38 weeks, was by Caesarean section.

The MSP, who is married to Professor Brian Ashcroft, the economist, said she was "overjoyed" at becoming a mother for the first time at 42.

Weighing 6lbs 1oz, Michael AlexanderAshcroft was born at 9.22am, and was followed two minutes later by Caitlin May Ashcroft, who weighed 5lb 10oz.

Ms Alexander's younger sister, Sue, also has twins.

In a busy day for budding political dynasties, David Cameron, the UK Tory leader, became a father for the third time at the age of 39. His wife Samantha, 34, gave birth to a 7lb 13oz boy at 11.55am.

Mr Cameron was called out of a shadow cabinet meeting at the Commons to be at her bedside in St Mary's Hospital, Paddington, for the delivery.

The baby was born slightly earlier than expected by Caesarean for medical reasons - the births of the Camerons' three-year-old son Ivan, and two-year-old daughter Nancy were also by Caesarean.

Mr Cameron said the family had not decided on a name yet, joking: "I can't make decisions like that. He's lovely, he has blue eyes and black curly hair.

"It was all over very quickly. Sam is doing really well, she's sitting up and will be here for a couple of days."

Mr Cameron said he intended to take two weeks' paternity leave, leaving William Hague, the former Tory leader and shadow foreign secretary, to stand in at prime minister's questions today.

Rosemary McKenna, the Labour MP for Cumbernauld, Kilsyth and Kirkintilloch East, accused Mr Cameron of "duplicitous opportunism" for going on leave, as he had fought Labour plans to extend it for fathers, but other MPs were more generous.

Speaking in the Commons, Patricia Hewitt, the health secretary, said: "We all wish [Mr Cameron] well, both as a parent and in his efforts to give up smoking."

Ms Alexander plans to stay a few days in hospital to recover.

She said: "We are overjoyed at the birth of our twins. In particular we should like to thank Dr Alan Mather and the entire team at the Princess Royal for all the support and professionalism they have provided over recent weeks and months."

Professor Ashcroft added: "Michael, Caitlin and Wendy are doing well. We are thrilled and excited by these beautiful additions to our family, and grateful for all the good wishes we have received."

The Rev Douglas Alexander, Ms Alexander's father, said he and his wife Joyce were delighted with the birth.

"I'm delighted for Wendy and Brian and looking forward to the twins growing up and joining in with the other grandchildren, just like any grandfather would be, " he said.

Last week, Ms Alexander admitted wrestling with her conscience over having a Caesarean, after seeing it described in some books as "a second class birth".

However, she said she later realised there was no such thing, and followed her doctor's advice.

There is no set maternity leave for MSPs - it is by negotiation with party managers - but Ms Alexander is expected back at Holyrood before the summer recess.

A former adviser to Donald Dewar, she became an MSP and minister in 1999 under Mr Dewar, moved to enterprise under Henry McLeish in 2000, and was effectively shown the door by Jack McConnell, who burdened her with an impossible workload of 13 briefs to oversee.

She quit the cabinet in May 2002.