.uk Best place to sell .co.uk names...

It works itself, if domain is quality.
Marketplace is not needed, except you want to sell to another domainers.

domainlore.co.uk (Auction platform) if you have domains that you think other domainers may want. Expect domainers prices though. Some good sales for the very top-notch single words, which then attract Investors into the auction.

Otherwise, it's really just a case of following the same avenues as for other Global domains. ie, your own landers, Sedo etc. Always set your pricing in UK Pounds

You'll probably notice a lot of overseas sellers mistakenly register and expect to sell US spelling for UK domains - (Probably because they see every major extension taken) They never sell, so check your word spelling

Wrong extension my bad.