Immediate safety advice
If water is near electrics, leave the area and contact your electricity provider immediately. Do not stand in standing water or touch switches.
To stop water flow: locate your internal stopcock — usually under the kitchen sink, near the water meter or in a downstairs cupboard — and turn it clockwise until it stops. Open a cold tap on the lowest floor to drain pressure from the system.
Place buckets under active drips, lift rugs and electricals, and photograph the damage for insurance before we arrive.