Generally speaking in the UK, a no claims bonus is a discount given by an insurance company to a policyholder who does not have claims on their policy. Typically the discount starts around 15% for 1 year of no claims and can reach up to 65% after 6 or more claim-free years, depending on the insurance company's guidelines.

Thus the more years you have no claims, the cheaper your premium will be for the car that you need to insure. If you have gone many years without claims and then place one with your insurance company, the no claims bonus might only be bumped back and not completely wiped out.

If your insurance pays out a claim for the damages caused by the accident in your girlfriend's vehicle then you would likely lose some of your no claims bonus. If instead your girlfriend's insurance is paying out the claims for the accident, it would be her insurance and no claims bonus that would be affected.

As for being charged with drink driving, while you may not lose your no claims bonus your insurance company will likely raise your overall premiums by quite a bit. Drink driving convictions are considered to be very serious to UK car insurance companies and some insurance carriers might refuse drivers full insurance.