Originally Posted by
clubman
But why should MD be any different to any other European destination?
It looks like ET one way's have not been loaded which is why you only get offered CE, but maybe rules are different with MAD.
Well, the cynical explanation would be that IB and BA have no direct competition on the MAD route, and share all the revenues. If you don't have a direct competitor then your incentives to offer cheap one way fares (for example) declines dramatically.
Other airlines do fly to London from MAD (notably easyjet) but not to LHR.