Turning off mains stopcock

BilzM

Thank you all for your responses (and sorry for my slow response!). I called United Utilities who came out to take a look. It turns out the outside stopcock is damaged and so they're changing it (well, they've already started doing some work on it).

Regarding the water tank, just for closure :
a) I have just last month got rid of my old water tanks (cold water, central heating, and big hot water cylinder) and replaced it all with a combi boiler
b) I think the increased pressure from the combi boiler is what has caused the leak in my hot water tap

Oh, and a friend lent me his stopcock tool. It didn't fit. Pretty sure an allen key was sufficient.

P.S. no valves on the dripping tap, unfortunately.