Originally Posted by Raffles

South Ken is the most bizarre thing I have read on here for ages! It is as central as you can get. It is NOT about traffic congestion in Central London, it is about dealing with an 18th century street pattern, confusing signage, large numbers of one way streets etc. Not recommended.

Luton is by far your best bet. And last time I looked, First Capital Connect trains went to St P, London Bridge and quite a lot of other central places. They even go direct to Gatwick from Luton. I would get a hotel near St P or London Bridge and then you can easily get there from Luton and then easily get a trainto LGW next day.