Gas Leak in London: Exact Emergency Response Steps to Follow
A suspected gas leak requires an immediate and specific response. This guide sets out precisely what to do — and what not to do — if you smell gas in a London property, and how the emergency process works from initial detection to safe reinstatement.
If You Smell Gas: The Immediate Actions
If you smell gas in a London property, the first priority is to stop the supply and remove any sources of ignition. Do not turn any electrical switches on or off — both actions create a spark that can ignite accumulated gas. Do not use a mobile phone inside the property. Do not operate doorbells, light switches, or any electrical appliance. Open windows and doors to ventilate the space. Locate the gas emergency control valve — typically next to the gas meter in a cupboard, under the stairs, or in a meter box on the external wall — and turn it to the off position (the handle perpendicular to the pipe indicates off). Leave the property and call the National Gas Emergency Service on 0800 111 999 from outside or from a neighbour property. This service is available 24 hours a day, seven days a week, and is free.
Do not re-enter the property until the National Gas Emergency Service has attended and confirmed it is safe to do so. The National Grid emergency team will isolate the supply, test for gas concentration, ventilate the building if necessary, and issue a notice confirming whether the supply can be restored. They do not carry out repairs to internal pipework or gas appliances — that work must be completed by a Gas Safe registered engineer before the supply can be re-lit.
What the National Gas Emergency Service Does
When the National Gas Emergency Service attends, the technician will use gas detection equipment to locate the source of the leak. The leak may be on the gas main outside the property, on the service pipe running from the main to the meter, on the meter installation itself, or on the internal pipework and appliances within the property. If the leak is on the network side of the meter, the network operator is responsible for the repair at no cost to the property owner. If the leak is on the consumer side of the meter, including all internal pipework and appliances, the property owner is responsible for arranging and paying for the repair.
The emergency team may issue one of several notices: a warning notice if there is a suspected but unconfirmed leak that should be monitored, an at-risk notice if a gas appliance is found to be operating unsafely, or a dangerous notice if there is an immediate risk that requires the supply to be disconnected. If an at-risk or dangerous notice is issued for a gas appliance, that appliance cannot be operated until it has been inspected and either repaired or replaced by a Gas Safe registered engineer.
Common Causes of Gas Leaks in London Properties
Gas leaks in London residential properties most commonly arise from corroded or damaged supply pipework, failed connections at meter installations, poorly maintained gas appliances where seals have deteriorated, and flexible gas hoses on cookers or gas fires that have cracked or come loose from their connections. In older London properties, pipework may be copper or steel that has corroded over decades. In rented properties, poorly maintained gas cookers with flexible connections that have not been inspected for years are a frequent source of low-level leaks at the appliance connection point.
After the Emergency: Getting the Supply Reinstated
Once the National Gas Emergency Service has isolated the supply and confirmed the location of the fault, a Gas Safe registered engineer must carry out the repair before the supply can be restored. The engineer will pressure-test the internal pipework to confirm integrity, repair or replace the faulty section or appliance, and re-test after the repair to confirm the leak has been resolved. Only then can the meter be turned back on and each appliance re-lit. If the property has been without gas for several hours or overnight, the boiler pilot light or ignition may need to be reset and the system represurised before heat and hot water are restored. Prestige Engineers carry out emergency gas leak investigations and reinstatement work across all London boroughs, with Gas Safe registered engineers available for same-day attendance.