This afternoon I heard the sound of a tap running in the bathroom. Went in an nothing on, but a wet floor.
Rushed to workshop got a screwdriver, into downstairs loo and levered off a panel to shut a ball valve. Quicker than trying to get to the stopcock in the street.
Water pouring through a large area of the living room ceiling, mercifully missing most things of importance, but not good for walls and ceiling.
Damn – I need one of those 'easy fit' isolation valves.
Managed to narrow it down to the cold tap supply to the washbasin. I managed to lever off a few large tiles without breaking any, luckily the plasterboard behind them was soaked and not full height. Then some reverse origami (facilitated by a speedfit-t) and I got this out.

Can anyone suggest how the stainless steel braid got this hole in it? Looks like its been dripping for a while before it burst -see the corrosion.
Fixed now, but I think I might replace the hot tap connector as a precaution as it uses the same sort of connector.
Neil