BBC puts money on Prince William to marry Kate Middleton

When Kate Middleton was photographed with Prince William at the polo earlier this month, she was described by one newspaper as the "lesser-spotted Kate" because of the length of time that had passed since their last appearance together. However, according to the BBC, the couple will soon be announcing their engagement.

Mandrake can disclose that the corporation is making a programme about the pair's courtship, Their Story, which will be broadcast on the night that their betrothal is officially announced.

"Believe me, in these straitened times, we would not be spending money on this programme if we had not been assured that they were definitely going to get engaged," says a senior BBC executive.

A spokesman for Clarence House says it is aware of the documentary but declined to co-operate with the producers.

Officially, the BBC is, understandably, keen to play down suggestions that it has been tipped off.

"We plan ahead for different eventualities," says a spokesman, who is, though, unable to recall a single other occasion on which it has made such a programme.

"The relationship is an area that our viewers are very interested in." The spokesman declines to say how much the documentary will cost.