Of course they can. It is a pity they don't pursue rapes without independent evidence. That might free up some resources to deal with proper crime.
If you can get the details of the other driver though then that would resolve the civil claim.
Personally though I would go back and make the point that you are prepared to give evidence. Ask them why they need independent evidence.
What independent evidence do they rely on when they investigate these historical sexual offences?
They can bring prosecutions costing the country thousands of pounds without independent confirmation then although I suppose they would argue that is CPS not them.
What is happening here is that you are just plain playing second fiddle to accusers. It is not acceptable.