Other party claiming for old damage.

My car rolled backwards and hit the drivers side front bumper of a car parked behind. There were some paint / scuff marks on boths cars, but nothing that wouldn't clean off. On the passenger side of the same bumper there was already a large dent and crack in the bumper. The headlight on the passenger side was also smashed. I suspect the driver had an accident which was their fault and didn't repair the damage.

I have now been contacted by the owner informing me of quotes for a new bumper. I have photo's taken the day after the incident that show that there is no damage on the side I hit. I also took photo's of the old damage.

If this claim goes through it will affect my no claims and have higher premiums etc etc. They will get a new bumper therefore dealing with their old damage.

Is it worth me fighting this claim?