Powerline 200Mbps AV adapter with 4 ports - just picked one up for £29.97 PCWorld Barbican (London).
The matching single port unit was £19.97
Don't bother going to the Barbican branch (which has just reopened as a Currys/PCWorld in one - weird) because I bought the last ones!
Before people ask for proof, copies of the receipt, etc. I'm not going to bother with that... I know what I paid, and if you're lucky, other branches might have them too. Not showing online.
The SKUs are 106761 and 904085 for the 4 port and 1 port respectively if that is of use to anyone.