Emergency Gas Isolation in London Properties: What to Do and Who to Call

Emergency Gas Isolation: A London Resident's Guide

If you smell gas, hear a hiss from a pipe, or suspect a leak, acting quickly and correctly can prevent a fatal incident. This guide explains exactly what to do and how your property's gas isolation works.

Immediate Actions If You Smell Gas

1. Do not operate any electrical switches — do not turn lights on or off, do not press doorbells, do not use your phone inside the property. A spark from any electrical contact can ignite gas.
2. Extinguish naked flames — candles, pilot lights (do not relight them), cigarettes.
3. Open windows and doors — ventilate the property immediately.
4. Turn off the gas at the meter — see below for how to locate it.
5. Leave the building — do not re-enter until it has been declared safe.
6. Call the National Gas Emergency Service: 0800 111 999 — this is free, operates 24 hours, and is staffed by engineers from Cadent Gas (or SGN in parts of London south of the river). Do not call from inside the building.

Locating the Gas Meter and Isolation Valve

Victorian and Edwardian Terraces (Pre-1930)

The gas meter is most commonly located in a meter cupboard on the external front wall of the property, or just inside the hallway. In older properties, it may still be in the cellar or under the stairs. The Emergency Control Valve (ECV) — the main isolation — is the quarter-turn lever or T-bar handle on the incoming pipe, immediately before the meter. Turn it 90 degrees so the slot is perpendicular to the pipe: gas off.

Post-War Semis and Detached Houses (1945–1980)

The meter is typically in a purpose-built external meter box on the front or side wall, accessed by a key (often supplied by the energy supplier). The ECV is adjacent to or integrated into the meter assembly.

Purpose-Built Flats and Mansion Blocks

Individual flat meters are commonly located in a communal meter cupboard on the ground floor or in a riser cupboard on each floor. Each flat's supply has its own ECV. In larger blocks, there may also be a building-wide isolation valve in the boiler room or plant room — only building management or a Gas Safe engineer should operate this.

Modern New-Build Apartments

Many post-2000 London apartment schemes use communal boiler plants (heat networks) rather than individual gas meters. If your flat has no gas meter, your heating and hot water is supplied via a heat interface unit (HIU) — there is no gas to isolate at flat level. In a genuine emergency involving communal plant, contact building management immediately.

When to Call the National Gas Emergency Service vs a Plumber

Call 0800 111 999 for:

• Any smell of gas
• A suspected gas escape
• Carbon monoxide alarm activation
• A damaged gas pipe

The National Gas Emergency Service will attend, make the supply safe, and cap the leak. They do not carry out repairs or relight appliances — that is the work of your own Gas Safe registered engineer.

Call a Gas Safe engineer for:

• Appliance repair after the emergency has been made safe
• Reinstatement of a capped supply
• Gas safety inspection before re-energising the property