Don't Panic...as there is not much you can do tonight anyway. If you have an immersion I would turn it off anyway.
Supply from your attic tank to upstairs tap and hot tap in kitchen will dry up as the tank empties, due to flusing of loo's etc but there is usually enough water in tanks to cover breakdowns like this.
My first worry would be to have some buckets of water to top up loo cistern in case it runs out. Neighbours might help you here but you should be grand overnight unless you have visitors and a full house.
The frozen pipe/stop cock may start to thaw during tomorrow but other s are better able to offer you advice on this problem.
Good point if it the storage tank in the attic is empty, but chances are there'll be a few days supply provided you're a little sensible about useage.
Leo