Might be worth getting them out. If you cannot isolate your property in an emergency without turning everyone else off tell them you need your own stoptap. They should come out and fit you one of their nice new stoptap affairs in a plastic box. These come with plastic tails, so you could kill 2 birds with one stone here! They'll locate the main supply for you, and couple onto the existing lead either side of the new valve. You then know where the main is, can shut the supply to your property off, and have a nice plastic tail to couple to and run a new plastic service into the house 
Just make sure (if they fit a valve), its before the supply tees off on your property and not afterwards otherwise you'll still not be able to shut half the supply off..... I know of a property they went to to survey for a meter, decided it had to go internally where supply entered the house. Guy said there were 2 supplies, one into house, one to outside W.C. so needed 2 meters. I wasn't so sure, and checked. Turning stoptap off under the sink cut supply to W.C. as well, so had they fitted 2 meters, any water passing through the 2nd meter would have been charged for twice as it had already been measured on the 1st meter! Guy was sent back, not vey happy about it, but was forced to agree (after checking....) they did only need ONE meter......
Friends of mine found a leak under their floor, no-one (including A.W.!) knew where the stoptap was. A.W. came out and looked, (after trying to say it was groundwater...), and finally agreed there was a leak. Team duly turned up, excavated outside back door and fitted a new stopvalve box. It then aspired on further investigation (basically as although the supply was switched 'off' at the new valve, there was still an awful lot of water coming from somewhere....), the property was fed from a larger lead" 'rider main', running along the back of the houses. A.W. had fitted the stopvalve to the house supply, but there was a second feed to the position of the original outside W.C. The W.C. had been removed, and the floor concreted over to hide the evidence. The lead supply at been 'capped' by hammering the end flat and burying under the concrete. Must have been leaking for years......
Just make sure (if they fit a valve), its before the supply tees off on your property and not afterwards otherwise you'll still not be able to shut half the supply off.....
I know of a property they went to to survey for a meter, decided it had to go internally where supply entered the house. Guy said there were 2 supplies, one into house, one to outside W.C. so needed 2 meters. I wasn't so sure, and checked. Turning stoptap off under the sink cut supply to W.C. as well, so had they fitted 2 meters, any water passing through the 2nd meter would have been charged for twice as it had already been measured on the 1st meter! Guy was sent back, not vey happy about it, but was forced to agree (after checking....) they did only need ONE meter......Friends of mine found a leak under their floor, no-one (including A.W.!) knew where the stoptap was. A.W. came out and looked, (after trying to say it was groundwater...), and finally agreed there was a leak. Team duly turned up, excavated outside back door and fitted a new stopvalve box. It then aspired on further investigation (basically as although the supply was switched 'off' at the new valve, there was still an awful lot of water coming from somewhere....), the property was fed from a larger lead" 'rider main', running along the back of the houses. A.W. had fitted the stopvalve to the house supply, but there was a second feed to the position of the original outside W.C. The W.C. had been removed, and the floor concreted over to hide the evidence. The lead supply at been 'capped' by hammering the end flat and burying under the concrete. Must have been leaking for years......