It is very hard to sell .co.uk nowadays, especially if it's not a one-word. You can try at DomainLore.uk or by BIN in Afternic (I have sold a .co.uk in both venues, it is possible). On this forum, the domain would probably have no resale price. In any case, the target price for a successful sale would realistically be less than $500, and probably closer to $100.