The Queen Mother is also a member of the order

At a reception at Windsor Castle to celebrate her 50th birthday, the Princess, who has just returned from a working visit to Bangladesh and Nepal, told more than 500 guests from her charities and other organisations: "I've been a very lucky lady.

"To be able to be involved in so many organisations, that the country can be so proud of, has been a real privilege."

"I want to say a very important thank you to my mother and father.

"It's thanks to their example, their advice and their help that you are here tonight."

The Princess, who last year carried out 683 official engagements in the UK and on tours abroad, represents 233 organisations.

She has always displayed great courage and intellectual integrity

Mike Aaronson Save the Children

But she is probably best known for her charity work with Save the Children of which she has been president since 1970.

Mike Aaronson, director general of Save the Children, presented a birthday gift of two paintings of Scottish landscapes from her many organisations throughout the UK and overseas.

He paid tribute to the princess's "legendary hard work" and "obvious commitment" to the children's charity.

"In her readiness to think laterally and to question conventional wisdom - often through vigorous debate - she has always displayed great courage and intellectual integrity," he said.

It was an "extraordinary achievement" to exercise "inspirational leadership" for such a wide range of organisations, Mr Aaronson added.