New outdoor tap without turning off water.

[Brenhden]

These are great options. I'll try and find the main supply again...

I think what he means is cut into the mains pipe outside whilst it's live and then have a pre-built tee with a tap on it, then all you'll have is water running in your garden until you get the tee fitted then close the tap. Then just re-connect your house supply.

Either that or get everyone in your lane involved and see if they have a means of isolation for their own property, if not then just notify that the main supply will be shut off for the short duration to have an isolation point introduced.

Either that or shut off your house mains supply and run a new supply pipe into your workshop.