Very sorry to see that but at the risk of being flayed, I would be tempted to see if your dent man can get that out and if can and its say £50 worth I would be tempted to put it down to a lesson learnt and leave it at that with no insurance involvement, and remember not to leave your car in quite such a vulnerable location in the future. Easy said I know, but the principle is the same as supermarket car parks where we far park as way from potential damage situations as possible.
On the other hand if the dent can't be got out then I expect you are into mega hundreds for a fix and yes, you ought to push for a Court Order for payment.
If you are not with Direct Line hopefully it should not affect your NCB. But you will still have to declare it as a 'claim' on each renewal but hopefully with a Court Order confirming it was vandal damage that should not affect your future premiums. Good luck with the outcome