dont know what system you have but guessing from words in your post- you have electric heated (2 emersion heaters, 1 off peak) open vent hot water cylinder (living in flats?).
turn off power to them both at fused spur or electric box. if by bottom front left you mean lower emersion leaking then you need to get someone out as you need the cylinder drained in order to repair.
could be related to overflow problem if emersion has failed and is constantly heating cylinder but either way you'll need someone out. you could have 210 litres of hot water in there.
if it is how ive assumed then you could isolate mains cold for tonight and lay towels and trays to catch water pressuming its a relatively small leak and get someone to look at it soon as practical. if it is emersion leaking you'll need cylinder drained.
dont know if ive guessed right but thats the impression i got from your post
iain
June 2008