"Chessington, which while strictly speaking counting as greater London would be considered more a day trip venue by most of the capital’s residents."
Utter nonsense. Chessington is a 35 minute train journey form Waterloo. I know. I live there. I commute to the other side of the capital most days. Many's the time I come back from work, change and then go straight back into London. Yes it is the outer edge of the London conurbation, but we're not talking San Angelean scales of urbanisation. Remember that the M25 is only about 127 miles point to point, and that skirts the whole thing. It's only a "day trip venue" if you're hinting at the so-called World of Adventures.
Chessington is actually a very appropriate location for London access, particularly if you take maintenance and supply into consideration. Granted the rail connection is only a half-hourly service (serving both the Chessington stations, and Tolworth which is actually closer to most of the industrial estate), but it is situated just off the A3 - a major arterial route straight out of London, and is within ear-shot of the M25 which is also only 5-10 minutes distant, 12 miles as the crow flies from the centre. Digital Realty have a co-lo site here for that very reason.