So my P7 [helmet] torch had started cutting out intermitently (which may have been heat related) and I was on the brink of sending it back. But I thought I'd have a quick look.
When I got the brass pill out of the battery tube I saw this:

The black wire is the positive feed from the battery (no driver on this torch it turns out) and the negative is from the circular tab with the screw through into the brass pill/heatsink.
Originally I thought that the wire was at fault as the torch flashed whenever I touched it. But I finally discovered that the issue lay with the circular negative contact. For some reason the light would go off when the contact was pushed down (i.e. when the screw was tightened), but it would work fine when the contact was lifted up but the screw was still making contact with both the circular contact and the brass pill/heatsink. So I presume there was some short going on.
So I got a very small piece of plastic, made a hole in it for the screw and used it between the contact and the led base.
End result it that it's now working perfectly. Below are two pics of the [blue] plastic insulator in place – one bad and one better, but I hope you get the idea.
If you've got problems with a similar torch it might be worth giving this a try. 🙂

looks like a good job, well done for finding out what the problem was.