putting the car away to night i managed to scrape the left front on a fence.i've got touch up paint and sorted the small scratch on the colured bumper but the black curved plastic bit on the bumper is damaged.

would it be best to fix it,replace it or just leave it ?

it's a 56 reg.

Hey I've done the same to mine. The paint has come away and the black bumper looks white but I'm going to try and wet sand it away with 2000 grit sandpaper, lots of water and wahsing up liquid. Then using a porter cable and meguiars scratch x to buff the sanding marks off. If you havent got a polisher you can try scratch x by hand. Its harder but will still do the job.

Depending on how bad the bumper is, it might be worth giving wet sanding a go.