Prince William and Kate Middleton do not have the gravitas of traditional royals and are simply "celebrities", a British historian said today.

Christopher Lee, who wrote the definitive Radio 4 British history program This Sceptred Isle, said the Duke and Duchess of Cambridge should be lumped in the same category as David and Victoria Beckham.

"I don't think they rate with the Beckhams, but I put them in that slot," he told the Daily Mail.

Lee, an ex-BBC defense correspondent, says the couple do not have the "gravitas" to be anything other than celebrities.

He added: "They love bending down and talking to kids and doing ordinary things.

"They are ordinary, but they are celebrities rather than old fashioned 'don't ask questions, don't touch me' royalty."

Lee said he thought the gloss was wearing off Kate Middleton and added that the couple would, in middle age, end up like royals in the Danish, Dutch and Belgian mould – "nice people but rather dull and inoffensive".

And while he believes Prince George may have some public role in 50 years’ time he doubts he will be the traditional King of England.