No Water after Mains Switch-off, What to Check?

[RealPolitik]

Is your flat on the top floor? Are your neighbours' on floors below?

The brief rush indicates that sufficient pressure is available, but that it's flow has been restricted.....a partial blockage.
You said several water board plumbers had attended, and blew air down the pipe. Was this compressed air flowing back towards the 'branch', and was the pipe at the branch open to atmosphere?

This flat is 1st floor and above - as far as I’m aware, the feed from the mains also supplies the ground floor commercial premises and two separate flats above a separate commercial property next door (shared flat entrance door and stairs, where the pipes are briefly visible, developed at the same time).

The compressed air was flowing back down towards the branch, but I don’t think the pipe wasn’t open at the branch/mains connection.

 

[MeldrewsMate]

The compressed air was flowing back down towards the branch, but I don’t think the pipe wasn’t open at the branch/mains connection.

If the pipe wasn't disconnected at the branch end then the compressed air isn't going to blow anything out because it wouldn't flow.

 

[RealPolitik]

My thoughts (but something, somewhere, moved because a little bit more water started coming out of the taps).