Here's an update:

I thought the quote looked a bit high - for comparison, in our own house a couple of years ago we had an old fuse board replaced with a new 18th edition consumer unit, a new circuit installed for a shed about 20 metres away using armoured cable and a small CU in the shed, earth bonding added to 18th edition standards and an inspection and test report done, all for about the same price. Anyway, I asked the agents for a second quote and (surprise surprise) it was nearly half the price, including another test report. This quote was properly itemised and the prices look reasonable, so I gave them the go-ahead for the work. Replacing the recessed R80 ceiling spotlights with fire rated GU10 units and an adapter would be a prudent move anyway, even if fire rated units aren't strictly needed. The second quote was for blanking off the cooker switch and putting it in the cupboard, and the price was reasonable, so in the end I thought it wasn't worth quibbling over.

Many thanks for all the advice

David.