Tom Anderson wrote:

AIUI, the East Brixton platforms were on the Atlantic lines, so presumably
wouldn't have been much use to this service, BICBW.

That's correct, East Brixton was a quite different station. The
Victoria - London Bridge service runs on the Atlantic lines, serves
Wandsworth Road and Clapham High Street, previously named just
'Clapham', and then crosses over the main lines on the high-level
bridge at Brixton, then heads towards Denmark Hill. East Brixton
station was at Barrington Road, a short distance to the East of where
the Atlantic lines cross over the main lines, above Brixton station.
There has been talk from time to time of building platforms on the
high-level bridge to serve these lines, as a replacement for East
Brixton, but it seems unlikely to happen.

The other route from Victoria to Denmark Hill is to run down the
Chatham main line, towards Brixton station, but just before the
platforms there to diverge left; it is on these lines, that I *think*
Brixton Station also had platforms at one time; i.e. it was a 'V'
shaped junction station. at this point these lines are heading East,
and the Atlantic lines come in to then run alongside them, towards
Denmark Hill. These tracks are the Northern pair, and the Atlantic
lines are the Southern ones. Both sets of tracks then cross over the
main Herne Hill - Elephant & Castle line, just South of Loughborough
Junction station. Just before they do so there is a spur from the
Northern tracks, i.e. not the Atlantic lines, to join the Loughborough
Junction line, just North of that station. There were platforms on
this spur, i.e. the Western one at Loughborough Junction, so if I am
correct in thinking that there were also platforms at Brixton on the
lines towards Denmark Hill, then the Victoria - Moorgate Street trains
would have passed through both, and they would have been very close
together. Whether they served both stations, I don't know. This was
fourty years before I was born.

The main line platforms at Clapham and Wandsworth Road are also long
gone; these stations are now served only by the Atlantic lines.