Taking photos on London Underground?

When the Blue Uniform takes you by the collar - that's when you know that it was not allowed.
Seriously, I would not try it without written permission from Network Rail and London Transport (or whoever it is these days) in my pocket. I would assume that anyone in a Blue Uniform has no knowledge of the current law (whatever it is) and will demand that you hand over the camera / memorycard / film / etc (assume no knowledge of the technology either)to them.
Not something that I would care to try.
Geoff

First thing to note is that there is no underground from Knightsbridge to Gatwick - you will need to take the train from Victoria Station (easier and nicer to get the bus from Knightsbridge to Victoria). You have the choice of the excellent but pricey Gatwick Express service, which is very frequent and takes 30 minutes, or other trains which stop once or twice on the way, which are also very frequent, somewhat cheaper, and take perhaps 10 minutes longer.

Second thing is that I think technically you need to ask permission to take photographs on the Underground, but you are unlikely to be challenged if you use a compact camera. The light is actually pretty bright in most tube stations so you shouldn't need to go above perhaps ISO400. I personally would not use an SLR in busy central London underground stations, but have got some great photographs with an old 5MP Panasonic LC1 - given that was a complete noise-monster, I am sure that your ZS3 should be able to cope pretty well.