Lots of different firms, quite a variety of prices, varying degrees of facilities
for .co.uk, .org.uk, .ltd.uk or .me.uk I would recommend one of the big UK firms, such as ukreg.com or 123-reg.co.uk
Most pricing is from 5 to 10 pounds +VAT with a UK firm, for a .uk domain.
Re e-mail, assuming you have an existing mail account (either with ISP, or Hotmail / Live.co.uk / GMail / Yahoo / OperaMail or a paid-for service such as FastMail.net, Runbox.com, MailSnare.com) most offer free mail forwarding, but here are some findings:
uk2.net allows @ domain as a POP mailbox
plus 5 different addresses to be forwarded to that mailbox
virtualnames allows * @ domain up to * @ domain to be forwarded (to an existing mail account)
123-reg appears to offer a single mail address to be forwarded to an existing mail account
ukreg seems to offer forwarding of @ domain to be forwarded to your existing mail account.
I would avoid 1and1.co.uk (show monthly prices, seem to charge some services for full 12 months in advance, and when I used them, seemed to make cancellation a jump through hoops).