Updated

Former Prime Minister Margaret Thatcher had to skip a reception Thursday to honor her 85th birthday because she was ill with the flu.

Prime Minister David Cameron read a note of apology from Thatcher to 150 friends and colleagues who had gathered at 10 Downing Street — the official prime ministerial residence — for the event.

"I hope that you will appreciate that on this particular occasion I have had to accept that the lady is not for returning," Thatcher joked, Cameron said. In 1980, when she was prime minister, Thatcher said defiantly that "the lady's not for turning" as she stressed her determination to stick to her tough economic policies.

The former Conservative leader turned 85 on Wednesday. She has suffered from a series of health problems in recent years.

Cameron's office said another party with a similar guest list will be held once she has recovered.