The Queen was recovering in hospital last night after keyhole surgery to remove torn cartilage from her right knee.

The 45-minute operation, at the King Edward VII Hospital, central London, went "very well", Buckingham Palace said.

The 76-year-old monarch was expected to be "fully active again within a few weeks", said the Palace.

The minor operation, under general anaesthetic, came after the Queen wrenched her knee while walking on uneven ground during a private visit to Newmarket on the Friday before Christmas.

She was admitted to the King Edward VII on Sunday night and is due to remain in the private hospital until this morning.

The operation follows a scan on the troublesome knee last week at King's Lynn Hospital, near the Queen's Norfolk estate.

She had been in some discomfort over the Christmas period when she walked with the aid of a stick.

"Her Majesty will rest at Sandringham over the next two weeks and will then resume a limited programme of engagements," said a Palace spokeswoman.

Standing would have to be minimised so it might be necessary for investitures, early this year, to be performed by another senior member of the Royal Family, probably the Prince of Wales.

The operation was performed by the Queen's orthopaedic surgeon, Roger Vickers.

It is a rare hospital stay for the Queen who, it is thought, was last admitted overnight in 1982 when she had a wisdom tooth extracted at the King Edward VII.