You can't legally do your own electrical work? Shiver...
It's not actually illegal to do your own electrical work, though you'll need to get some types of work inspected. HOWEVER, your insurance company will absolutely seize on it as an excuse not to pay if your house burns down (most insurance policies will require that anything but the most basic work is done by qualified people).
At least it’s not as bad as in the US. As I understand it you only need to get it inspected and signed off by a licensed electrician if you DIY, no need for permits from the local council.
You can if you're a qualified electrician. Or if not do it yourself and get a qualified electrician to approve it afterwards.
Depends. You can certainly replace broken or worn socket/switch faceplates.
We were running spurs from the ring main and adding new outlets which is definitely not allowed without inspection now.
It’s really not that complicated and I’d feel completely comfortable doing it myself today but I understand how that may not be true for everyone so the requirement is probably reasonable.
Spurs have been re-legalised: the Part P changes have now been rolled back to whole new circuits, and spurs and new outlets are back as non-notifiable along with new faceplates etc.
That said, you're theoretically supposed to do a full set of earth resistance measurements etc. on the new wiring, which is hard if not impossible unless you've got proper electrician's test equipment. But in reality no one does that when DIYing it.