The driver ethandron is referring was a totally different colour to the foreign national they claimed was driving as the photograph proved. He did go to prison.
Here is another case with a hefty fine and suspended prison sentence:
http://www.telegraph.co.uk/news/uknews/1584807 /Speeding-ticket-couple-blamed-offence-on-frie nd-in-Australia.html
And another one sent to prison:
This month, a nurse was imprisoned for six months for trying to blame a speeding offence on her former sister-in-law, who lives in America. Joy Rees, 39, was caught at 51mph in a 40mph limit in Plymouth last July
http://www.timesonline.co.uk/tol/news/article7 24848.ece
So you absolutely must get all the necessary details from your friend - remember, the authorities can and do check with the airports so give the flight date and name at the very least.
Hopefully the camera will prove you weren't driving but there have been several cases where the registered keeper has named a foreign national to protect a relative/friend living in the UK, so give them every fact that you can.,