Hi folks, after constantly hearing like a 'tap has been left on', have replaced tank in loft ball etc. But it still goes on.  Outside stop cock ceased noise, however, internal stop cock old and just turning 'i.e. old and not working'.  No water showing anywhere downstairs or even the garden. The question is: do I call out Water supplier, or rip out kitchen work units to get to stop cock to try and start locating the leak?  Not on a meter either (good job at the mo as well).  House is approx late 1940s

Normally the pipe from main to your house is your responsibility. You could call the water co but they are likely to be more expensive than another contractor. The water co is likely to use a contractor anyway.

Is it possible the stopcock outside feeds more than one house? Leak could be next door!

Perhaps check the loo or garden tap in case any of those have been plumbed into the incoming.

Is the heating system a new sealed system? Perhaps the filling loop is open and it's pushing water out of the Pressure Relief Valve?

Not good to let this go on for a long time as quite possible for a leak to  affect the foundations.

Go easy today. 30C predicted for some parts of the country.