I loved that film! I was obsessively trying to find out where the park was that Mendel tailed the woman. I am sure it was definitely not on Clapham Common but at the beginning of the scene you can see the name of the close that she lived - I am sure I found it in the A-Z in the London suburbs.
The scenes with Scarr were filmed in the Chelsea/Clapham area - the balloon tavern which is near to the Chelsea Conrad complex has recently changed into a swanky restaurant. Also Mason's flat is near the Albert embankment bridge in Chelsea.