Sorry Kempie's right
http://www.cps.gov.uk/legal/section9/chapter_a .html
Offences of causing or permitting the uninsured use of a vehicle should be regarded as being as serious as using a motor vehicle without insurance.
Now this is a bit of a long shot but
A statutory defence is provided by section 143(3) RTA in relation to a driver who unwittingly drives his employer's uninsured vehicle.
You could perhaps try to claim a defense under this that you believed it was covered under the employers insurance
But really the friend was driving without the owners (you) permission wasn't he?
It's getting rather complicated - hopefully the police and CPS will think so too and won't come after you but if they do I'd get some legal advice if I were you