I guess my question was more how would they know? If I make my own way from Iceland to the UK and then leave the UK as a continuation of my journey albeit from LHR there would be gap no flight.you are allowed no more than one stopover *and* two transits in any one city (except your country of origin!) So you could have stop in London on the outbound, and then transit - less than 24 hours - on the way back.
I am trying to be too clever or would that work?

