London ? Although she has grown frail after a series of small strokes, Margaret Thatcher commanded the room when she arrived – about 15 minutes late – to a bash Thursday to celebrate her 80th birthday. The delay, said an aide, was because she took a congratulatory phone call from President Bush.

Wearing a navy blue coat and dress, a string of pearls and – as always – a matching handbag, her trademark, the former prime minister smiled and paused for photographs before making her way into the plush Mandarin Oriental Hotel near London’s Hyde Park.

Fifteen years after leaving Downing Street, Thatcher remains a powerful force in Britain, particularly among her party faithful.

Although more reclusive in recent years – she has given up most public speaking on her doctors’ advice – Thatcher’s reception Thursday was testimony to her lasting legacy as Britain’s first female prime minister, nicknamed the “Iron Lady.”

Heading the high-powered guest list were Queen Elizabeth II and her husband, Prince Philip; Prime Minister Tony Blair; and Sir John Major, Thatcher’s immediate successor at No. 10 Downing St.

The queen shook Thatcher’s hand on arrival.

Another guest, actress Joan Collins, said she adored Thatcher.

“She is the ‘Iron Lady,’ and I want to be just like that when I grow up,” Collins said.

Among the more than 600 guests invited to the party were many members of Thatcher’s Cabinets and two current candidates for the Conservative Party leadership, David Davis and Liam Fox, Penrose said.

The other Tory contenders, front-runner David Cameron and Kenneth Clarke, were not asked to attend, prompting speculation that Thatcher was quietly taking sides in the race to head the party. Penrose said Thatcher did not intend the guest list as a comment on which candidate she preferred.

Caspar Weinberger, former President Ronald Reagan’s defense secretary, was the most prominent American politician invited.

Missing was former Soviet leader Mikhail Gorbachev – of whom Thatcher once commented “we can do business together” – but he was scheduled to meet her during a London visit next week.

Thatcher’s twin children, Sir Mark and Carol Thatcher, were at the party. Mark Thatcher pleaded guilty in South Africa last year to unwittingly helping to bankroll a failed coup in oil-rich Equatorial Guinea, in West Africa.

Also invited were composer Andrew Lloyd-Webber, writer Frederick Forsyth and best-selling novelist and Tory peer Jeffrey Archer, who spent two years in jail for perjury and obstructing justice.

Earlier Thursday, Thatcher’s assistant Gilly Penrose said the former prime minister was feeling good about her milestone birthday.

“Her house is looking like a florist’s and she’s very much enjoying it,” Penrose said. “She’s very philosophical about (her age), because she’s very active still.”