Queen prepares for knee operation

The Queen walked inside unaided

The Queen has been admitted to hospital to have a torn cartilage removed from her left knee.

She arrived at King Edward VII Hospital in London at 1900 GMT and will have key-hole surgery on Friday morning.

The Queen, who appeared to show little discomfort on arrival, had a similar operation on her right knee in January and is expected to recover fully in weeks.

She plans to spend Christmas with her family at Sandringham as usual, a Buckingham Palace spokeswoman said.

"The Queen is expected to leave hospital some time during the weekend and she should be fully active again within a few weeks," she added.

The spokeswoman said Friday's surgery had been arranged following her first knee operation in January and was not the consequence of a fall.

BBC correspondent Nicholas Witchell, outside the hospital, said the Queen did not seem to be in any pain as she got out of her car and walked into the building.

The initial surgery was undertaken after the Queen jarred her knee while walking on uneven ground during a private visit to Newmarket last Christmas.

At the beginning of this year when she came out of hospital, she did look as if she was having a few problems BBC correspondent June Kelly

The 77-year-old has enjoyed robust health throughout her life.

"At the beginning of this year when she came out of hospital, she did look as if she was having a few problems, but she looked in fine form the other day when meeting the rugby players," BBC correspondent June Kelly said.

An investiture ceremony at the Palace, which saw England rugby hero Jonny Wilkinson receive an MBE, went ahead on Wednesday.

But the Queen has pulled out of two other public engagements planned for this week.

They are a carol concert hosted by the Women's Royal Voluntary Service (WRVS) on Thursday in London and the re-dedication ceremony of HMS Invincible in Portsmouth on Friday.

The Duke of York will attend the latter event instead of the Queen.

The Queen's commitments planned for next week, including receiving credentials from two new ambassadors, will be postponed or cancelled.