Maybe I've invented something. I was thinking about those washing
machine hose connectors that you clamp round the copper inlet pipe,
tighten the screw and a sharp-edged pin forces a hole in the pipe.

Then while I was pondering the need for a isolating valve under the
kitchen sink, I thought, now wouldn't it be wonderful to have some
kind of similar gadget that you just position around the pipe, tighten
one or more screws and hey presto, an instant gate valve! You could
install one without even turning the water off.

MM