If you suspect it may be worth something why not just buy the domain name[s] anyway ?
The cost of a .com and .co.uk combined will hardly break the bank and once you buy them you can attempt a resale as soon as they are registered.
The .co.uk will typically be far less desirable than a .com or .net address.
It's a tiny amount of money to invest so if you suspect there is any return in it I'd just go for it.
I have no idea how to find out the net worth of a domain that has not been registered but I wish you every success.