There should also be a stopcock outside the property as well. Usually under a small plastic or (if you have a really old one) pear shaped cast iron cover in the path outside your property. You should have a proper key to reach into the hole (the tap is about 2' down), but a bit of wood with a notch cut in it will do. Lots of stopcocks have been replaced by water meters (usually under a 6" dia round plastic cover) which also incorporate the stopcock. For most domestic 'emergencies', use the one under the sink, but it is worth finding out where your outside stopcock is as well; just in case.