This has been asked before,I think there are only two underground stations with a 7,6 format and don't know the answer.
CLAPHAM COMMON
or RUSSELL SQUARE
Thanks so much EB, pastille & samak for your help it seems to point towards Clapham Common I think, will only discover if that is correct on return of the answers.
Might be worth checking on Answerbank....because this was intriguing me, I went on today and there is a lively debate...Other options were given, can't remember what...I think more people than you are confused.
Just looked on answerbank and I am even more confused.EB is of-course right with Warwick Avenue but answerbank is suggesting Crystal Palace which is not on the underground.I think I'll sick with this site.