Took me six weeks to validate London Tower (now Heathrow)..... but somebody will probably spoil it all by saying "but it's busier now"!! (And I'd definitely fail nowadays)
Seriously, I spent a year at Kidlington before going to EGLL and the intensity of the R/T at 'TK definitely helped. The other significant factor was that I spent much of my childhood as an avid a/c spotter, spending many hours at LL so I was very familiar with procedures before I started. But then I am also superhuman....