I would suggest that you go with a UK registrar for .co.uk domains. It is cheaper and they know what they are doing in regards to dealing with Nominet etc.
I can highly recommend Domainmonster, great support, full control of your domain and a decent price at about £3 per .co.uk domain per year, (or as low as £2.57 if you renew in bulk).
I am not associated with Domainmonster in any way; I just had good experiences with them.
Added: I just realized that this thread was about the value of .co.uk domains and not about registrars. In my view .co.uk has a bright future as more and more Brits are getting fed up with finding US results in the Serps and gravitate towards UK websites hosted on .co.uk domains.