Thanks for putting my mind at ease, guys. The new battery is due to be delivered tomorrow. I found my dad''s old battery terminal cleaning brush in my shed, so I'm pretty much set for this job on Saturday. 

Had the new battery delivered and gave it a once-over. There's some slight pitting on the positive terminal and some very slight discoloration at the bottom of the negative terminal. Is this anything to worry about?

No, that's not a problem.

All done. Spent a bit of time cleaning the terminals thoroughly with some baking soda/water mix and a wire brush - they came up like new! Then coated them with some white lithium grease. Quite pleased with it - now I know it's been done properly and the terminals are fine.

they do like like new. and to think, you were convincing yourself you needed new ones.

8 hours ago, isetta said:

they do like like new. and to think, you were convincing yourself you needed new ones.

Yeah lol - was worried the terminals had started to corrode but turns out it was just old grease and dirt but it came off quite easily. I read in the Haynes Manual about letting the car sit at idle and wait for it to reach operating temperature so that it can relearn; I let the car sit for 5-10 minutes and it reached about a quarter of the operating temperature before I took it for a drive. Did I leave the car idle for long enough or would it be worth disconnecting the battery, reconnect it and let the car sit for longer?

I wouldn't worry about it.   You certainly did a good job on those terminals.