I'm amazed at people's use of the word urgent. Maybe its me, urgent is I've got water coming through my ceiling, my stopcock won't turn off and theres water everywhere etc.
First of all, the maximum time you wait for the water authority to replace the outside stopcock is 21 days. (in Essex) normally its quicker than that. If you want to pay for it, its a same day service.
Secondly, I am not aware of any T piece that you can fit to lead.
Thirdly, you'd need to use a leadlok which then goes into copper, you can then t off of this.
I'm presuming you have got an electric shower, this should be fed off the mains anyway. An electric shower should never be fed off of a tank. The require a minimum of 1 bar of pressure, although having said that you could achieve this if the tank was 10m high........ If you haven't got an electric shower you shouldn't connect it to the mains.
If your doing this yourself and your adept at diy then change the lead to copper. I suppose if its urgent you could freeze the mains but personally I wouldn't. Why take the chance.
