Prince Harry is not the cadet shown in pictures taken by The Sun newspaper in their infiltration of Sandhurst, Clarence House has said today.

A story published in this morning's newspaper described how a reporter penetrated the military academy where Prince Harry is a cadet, and spent seven hours wandering the grounds carrying a fake bomb before being challenged by a soldier.

The revelation prompted Dr John Reid, the Defence Secretary, to launch an urgent investigation into security procedures at Sandhurst.

But this afternoon, a spokesman for Prince Harry said that the prince is not the cadet shown in photographs and video footage taken by the newspaper.

"Basically, we were asked whether we thought it was Harry in the video," the spokesman told Times Online. "We've reviewed the footage and asked Harry and friends that were with him at the time and we believe it isn't Harry in the video."

The spokesman said that this does not detract from the overall point made by The Sun's story but that nevertheless Prince Harry could not be the cadet pictured: "We aren't making a big song and dance about it, we were just asked what we thought," said the spokesman.

"Those aren't the accommodation buildings that Harry uses and he wasn't carrying those bags at that time."

The Sun retorted that it was sticking by its story, insisting that the tall cadet in its video was the prince. A spokeswoman for the newspaper said: "The footage is Prince Harry. We stand by it 100 per cent. The Clarence House denial is absurd."

Earlier today the Defence Secretary said that the failure of security at Sandhurst was extremely worrying. Dr John Reid said: "I have demanded an immediate investigation into this serious security breach. I have instructed Sandhurst to change their procedures to prevent a recurrence."

The Defence Secretary told Sky News this morning that the breach showed that security arrangements at the Royal Military Academy, where Prince Harry is training as a cadet, were not good enough.

"I do not think there was an excuse for it happening, I think I've made that plain," Dr Reid said. "Let's find out what went wrong and let's put it right."

Dr Reid refused to criticise The Sun for its story. "I have no complaint about The Sun did, all it did was highlight a problem that should not exist," he said.

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