A stand-up paddle boarder has been picked up 11km off the coast of Dover in the United Kingdom, wearing just a hat, fleece jumper and shorts.

A UK Home Office spokesman says the man became disorientated while paddling, but witnesses and government officials have conflicting accounts of what happened.

The man was spotted by divers off the coast of Dover at dawn local time.

"The man was a German tourist in distress but who was in the country legally - he was not an illegal immigrant," the Home Office spokesman said.

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"He had been on the water for some time having gone out on his paddleboard and was picked up by HMS Valiant."

But Nigel Scutt, a marine researcher who runs the Dover-Marina.com website, said: "He said he had made his way across the channel from France, leaving at about midnight.

"The divers saw him at about 7.30am, so he was probably just over halfway towards the UK.

"There is quite a lot of this going on, but it is a polarising issue so the Government does not want it known."

- PA, AAP