The first 60 seconds
1. Turn off your internal stopcock. Most are under the kitchen sink, in the airing cupboard, or in the downstairs WC. Turn clockwise to close.
2. If you can't find or turn the internal stopcock, find the external stopcock. It's usually under a small metal cover near the front boundary of your property. You'll need a stopcock key or a long screwdriver. Turn clockwise.
3. Open every cold tap in the house to drain the system down quickly. Less water in the pipes = less to leak.
Minutes 1–5
4. Turn off the boiler and any electric water heater.
5. If the leak is near electrics, switch off that circuit at the consumer unit. If water is dripping into a light fitting or socket, turn off the whole consumer unit.
6. Move soft furnishings, electronics, and rugs away from the leak. Towels and buckets to contain.
7. Photograph everything before cleaning up. Insurance will want this.
Calling the plumber
Tell them: where the leak is (which pipe, which floor), whether you've stopped the water, whether you've turned off electrics, and whether anyone is in danger. Have your address postcode and a clear description ready — saves precious minutes on dispatch.
While waiting
Keep buckets emptying. If water is coming through a ceiling and bulging the plasterboard, push a screwdriver up through the bulge into the bulge — controlled drainage stops the whole ceiling collapsing. Catch with a bucket below.