Minor accident - advice wanted re: liability dispute

[se9boy]

Can anyone help with some advice please. Girlfriend had a minor knock in her car last week - she's negotiating a hair pin bend [uphill], guy comes down the hill, loses traction and skids into the side of her car. He admitted liability at the scene [no witnesses of course] and then proceeded to tell his insurer that she drove into him. I guess we're now in a 'knock for knock' situation.
Fortunately, she has protected NCB and only a £75 excess but I fuming that this little scrote has lied so blatently and want to know what I can [legally] do about it.
Is there any mileage in forcing the issue with our insurer for them to fight the claim or should I just give it up, lose the excess and wait for a higher premium next year?

[se9boy]

Thanks for the advice from all.
I contacted the insurer yesterday and told them I wanted them to refute the 3rd party claims and fight the case - they've told me it will be their decision as to how liability is agreed. So read into that "if it takes them more than 5 minutes or costs any money to fight it then they won't bother and it's no skin off their nose if it costs their customer money both now and in the future" - great!
All I can do is write a 'matter of fact' letter to the insurance company and see what happens.