Found
this interesting link from the Cycling Silk blog (a "silk" is a prestigious UK lawyer). It presents some information on the question (asked on this thread previously) about whether NOT wearing a helmet can lead to a court ruling against a motorist being liable for injuries s/he inflicts on you.
In brief: no.
Slightly longer: you can be at fault, but because helmets have never been shown to be effective in reducing motor injuries it doesn't make any difference. If the motorist (or counsel) could convince the court that your injuries would have been less with a helmet then you might face up to 15% reduction in your claim.
Same material covered
here.