First off, our drive should fit two cars, but because there is a small wall (1m long, 0.5m high) we only park one on it at the moment.

We've always been meaning to knock it down, but just never got around to it.

This morning, I had a plumber round to do some work. This plumber is a friend of my parents, not a close friend mind, but someone they would have a drink with in the pub.
I've always had him round on a few occasions to do the plumbing work, and he is a decent guy.

Unfortunately, whilst he was leaving, he somehow reversed into the wall in question and knocked half of it down.

He did say he would get it fixed as he knows a few builders, free of charge of course.

Now given that we were planning to knock it down, what do you think I should do.
It's not really just a case of knocking down the wall and that's it because that would leave a step between our drive and the public pavement because the drive is higher.

Should I have notified insurance at all?

I would only inform my insurance if I was planning to claim.I have heard of the next year excess being affected-just by informing the insurance co. and without making a claim.
How about coming to an agreement and getting the builder to part pay for the work that you were originally thinking about doing now that It has forced the issue-I know that youre not thinking about screwing what you can out of the builder and he seems reasonable,but youve got an opportunity to make it work for you!

I think it would be fair to request it to be knocked down, cleared away and made good. But, if you are thinking he should do the dropped curb and pavement it would be pretty excessive.

no need to inform the insurance

Your lookin between £400 to £800 possibly more for a lowered kerb depending on your local council`s policy

Or tell him not too worry about it but to let you have the next job or two for free

Quality idea, that way he isn't out of pocket for what sounds like a genuine mistake, and you could get some potentially expensive work done for nothing... Everyone wins!