LONDON, May 11 (Reuters) - Britain's Prime Minister TonyBlair dreamt of being a rock star in his youth and the ambition clearly runs in the family -- one of his sons has just bought a drum kit.

The Labour prime minister, who has three teenage children and a baby, made the revelation in a television interview on Friday.

Blair, who rarely talks publicly about his family, told GMTV he had gone home last night to find "my middle boy had bought a drum kit. I think that's every parent's worst nightmare."

The 48-year-old prime minister also let slip that he still played the guitar after his days in his university band Ugly Rumours.

"I play sort of rock and roll, and I'm pretty useless at it," said Blair, who used to have longer hair than heavy metal frontman Alice Cooper.

Chancellor of the Exchequer Gordon Brown, who lives next door to Blair at Number 11, often jokes about the endless noise from his neighbours, saying "loud guitar music playing at all hours, and that's just the parents."

But Brown told a news conference on Friday that he was getting "no additional soundproofing" at his residence because of the drums.

Blair and his wife Cherie have four children: Euan, 17; Nicky, 15; Kathryn, 13; and Leo, who will have his first birthday later this month.