I think I'd just renew it. If you go to a main Post Office, they'll do your photo and check and send it. It costs £14 extra to get it all sorted out, but you'll get your passport back in a week or so.
No. From 1st May only. It's like filling in those forms on the plane before you got to Thailand but you just fill them in before you leave home now. It's really easy, so don't worry.