Hi, I have put a pick through a plastic surface water drain (I know, I know!), creating a 6x6cm hole half way along it's length. Can anyone tell me whether I can repair locally or whether I will need to replace the whole length?

There isn't going to be much pressure in a drain so you can patch it. I'd cut the pipe and install a hubless sleeve. You may even find a saddle collar with a rubber seal will work.