The Queen was forced to cancel a number of engagements on doctor's orders today.

The 80-year-old monarch has withdrawn from an investiture ceremony due to take place tomorrow and scaled back her appearances at other events through the week due to "continuing discomfort" in her back, Buckingham Palace said.

The Princess Royal has been drafted in as an emergency replacement for the investiture ceremony while the length of time she will spend at a St James’s Palace reception for the Campaign to Protect Rural England, planned for later the same day, will be reduced.

On Friday when the Queen visits Crawley, the Duke of Edinburgh will complete one of her afternoon engagements, said a Buckingham Palace spokeswoman.

The cancellations come after the Queen was last week forced to pull out of two events in two days with the same back problem.

She had to scotch plans to officially open Arsenal's new football stadium and also abandoned an afternoon at Newmarket races in Suffolk.

A Buckingham Palace spokeswoman said: "The Queen’s programme has been amended due to continuing discomfort in her back.

"She is continuing to have treatment for her back pain."

She added: "At this stage there are no plans to cancel engagements next week, we are reviewing things on a daily basis."

Amongst those due to receive honours at tomorrow’s investiture but miss the Queen are Rolf Harris, who will be awarded a CBE, and EastEnders actor Rudolph Walker, who will be presented with an OBE.

The Queen strained a muscle in her back while holidaying on the Balmoral estate in Scotland during the summer.

She was forced to follow her doctor’s orders just two weeks after returning to royal duties following her annual break.

Twelve days ago she flew back to the UK after her first trip to the Baltic states, a whirlwind tour of Lithuania, Latvia and Estonia.

Photographers on the Baltic tour noticed that she seemed to be stooping. The Queen is not thought to have suffered from back problems before, although back pain has dogged the Prince of Wales for years.

The Queen usually enjoys good health and rarely misses engagements. In June last year she cancelled several, including watching Prince Harry parade at Sandhurst, after catching a bad cold and suffering from a sore throat.

In January 2003 she had keyhole surgery on her injured right knee after she tore her cartilage when she jarred her leg walking on rough ground during a private visit to Newmarket, Suffolk.

During her convalescence from surgery the Queen used a walking stick and her official engagements were scaled down.

Later that year, in December, she returned to hospital for a similar operation on her left knee.

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