Tom,
I am just going through my first .co.uk sale at present and it is definitely much more timeconsuming than a .com / net etc as the transfer cannot be done electronically.
You have to contact Nominet (can be done by email) who then post out the required transfer form, to be completed and sent to the purchaser along with a written letter as well confirming your agreement for the name to be transferred. The buyer then has to fill out their part of the form, add their confirmatory letter agreeing to the transfer and send off the transfer fee to Nominet (the fee can be paid by either party but in a Sedo brokered transaction they insist that the buyer makes the payment). Only then can the name be transferred. Heaven help anyone who sells a .co.uk to someone outside the UK!!!!!
This sale was brokered through Sedo and they take a massive £100 ($180) minimum fee for a .co.uk sale but even so I will still have made a profit (not huge in £ terms but reasonable in % of purchase price as .co.uk names can be cheap to register).
Good luck if you decide to try your luck with .co.uk names.
DavidH