I would expect there would be a riser and off the riser each flat would spur off. Depending on where that spur is and where they have intercepted it to bypass the leak may be causing your issue.
I would first contact the management firm for the flats to arrange for somone to investigate further, as they will hold plans for the riser and then can contact the water board directly and agree on what needs to be done both short and long term.
If you are that way incline, see if you can trace the pipe yourself, I assume your stop cock is under the kitchen sink, are you able to see where the pipe goes (does it go directly through the floor, run along a wall, there is normally a communal cupboard where these pipes would noramlly lead to, can you access it, and determine the route your kitchen pipe would take to get there?
Please send some pictures and ill see if I can give you any further suggestions, however as this is the rising main its really in the hands of the agent who manages the communal areas.
Hello I am just following up from last week, do you still require assistance?
Ok Mark, would certainly be interested to know what they find.
With any luck your water will be back on this afternoon.
No problem, glad you got there, appreciate if you can rate the service received so I can close the case down.