the railway in question was the district line , running overground west out of hammersmith , and the arch was in mahalgrave mews , which was a little alley running off the north end of putney bridge road , not far from the one-way system and the beginning of that flyover that takes you to heathrow or bristol or cornwall , depending upon how much petrol you have and how unhappy you are with the congestion charge or the bankers bonuses or the turner prize .