Actually 757_Driver, there was a separate advert with the headline of "Heathrow's second favourite airline" which ran in addition to the one you mentioned.
It certainly appeared in The Sunday Times, The Sunday Telegraph and the Evening Standard. I think it may have been used as well on an outdoor campaign using poster sites.
Utterly bizarre copy though. Like a bad attempt to copy the Avis "we're number 2, so we try harder" campaigns of a few decades ago.