In practice ? The kitchen fitter. Some of the more competent ones are perfectly capable of installing fused spurs moving sockets and so on, but mileages vary, there are a good few funny looking jobs out there. In the perfect world part P requires a spark to either do or inspect for brand new cooker radials etc but in the private domestic who knows, I suspect a lot of stuff magically appears 'flying under the RADAR.'
Mike

When my kitchen was done, they brought in a young electrician to install all the sockets.  After that, the kitchen fitters did everything.

I am broadly with Mike, but otherwise, it depends ...

I assume that we are dealing with a new kitchen in an old house rather than a new build.

If new circuits or a substantial degree of re-wiring is required, I'd expect an electrician to be involved, but of course he or she could sub-contract to the kitchen company.

If it is a matter simply of ripping out the old appliances, worktops, and cabinets and replacing with new ones in the same place; I'd expect a kitchen fitter with a limited electrical ticket to do it.

I wouldn't expect a kitchen fitter to get involved with new over-the-counter sockets, i.e. new back boxes; but if it were simply a matter of replacing tired old white (yellowed) ones with fancy antique brass ones with USB sockets, the fitter can do it.

Jimi, why do you ask please?

I first fixed a kitchen and when I cane back I was expecting more of the appliances to be fitted. I should have communicated and clarified it with the customer, they put the kitchen in themselves. Ended up messing about for ages cutting away units for the hob and extractor fan. Think they thought I would be fitting the integrated fridge too. In future I'll find out who is doing what before quoting and ask to come back when just the units are built.

Bad luck!