A gas leak is a life-threatening emergency. This guide gives you the exact steps to take if you smell gas in your London home or rental property — what to do, what not to do, and what happens when the emergency engineer arrives.
If You Smell Gas — Do This Immediately
Natural gas is odourised with mercaptan — the distinctive "rotten egg" smell is added specifically so you can detect a leak. If you smell it, act immediately and follow these steps in order.
Immediate Actions (First 2 Minutes)
- Do not touch any electrical switches — do not turn lights on or off, do not press doorbell, do not use any electrical appliances. A spark can ignite gas.
- Do not use a mobile phone inside the property — go outside first, then call.
- Open all windows and doors — ventilate the property as quickly as possible.
- Turn off the gas at the emergency control valve (ECV) — this is usually next to the gas meter. Turn the handle 90 degrees so it is perpendicular to the pipe (off position). In London terraces the meter is often in a box outside the front of the property; in flats it may be in a shared meter cupboard on the ground floor.
- Leave the property — go outside and away from the building.
- Call 0800 111 999 — the National Gas Emergency Service (free, 24/7). They will attend within 1 hour.
What NOT to Do
- Do not light matches, lighters or candles
- Do not smoke inside or near the building
- Do not operate any electrical switches (including the fuse box)
- Do not attempt to find the leak yourself
- Do not re-enter the property until it has been declared safe
What Happens When National Gas Emergency Arrives
The National Gas Emergency engineer will:
- Use a gas detector to identify the leak location and confirm gas levels in the property
- Make the immediate situation safe — this may involve capping a pipe or shutting off supply
- Issue a warning notice if a dangerous appliance or installation is found — this may require the appliance to be disconnected before supply is restored
- Restore supply only once the immediate danger has been addressed
They do not carry out repairs — their job is to make it safe, not to fix whatever caused the leak. You will need to arrange a Gas Safe engineer to carry out the repair.
Landlord Obligations for Gas Leaks
When a tenant reports a gas smell, a landlord must treat it as a gas safety emergency — not a general maintenance request. The correct response:
- Instruct the tenant to follow the emergency steps above immediately
- Do not ask them to wait until normal office hours
- After the National Gas emergency engineer has attended and made safe, arrange a Gas Safe engineer to carry out any required repair promptly
- Do not restore gas supply until the repair is complete and certified safe
Frequently asked questions
What number do I call for a gas leak in London?
0800 111 999 — the National Gas Emergency Service. Free, available 24/7. They aim to attend within 1 hour. Call from outside the property on your mobile. Do not use a phone inside a property where you smell gas.
Can I turn the gas back on myself after a gas leak?
Only if the National Gas Emergency engineer has attended, identified the issue, and confirmed it is safe to do so. If a Gas Safe engineer was needed to carry out a repair, the gas should not be restored until the repair is complete. Never turn the gas back on after a leak without professional clearance.
What causes gas leaks in London homes?
Most common causes: loose fittings on gas appliances (particularly after DIY work — never attempt gas connections yourself), corroded or damaged gas pipework (common in older London properties), failed appliance components (cracked heat exchanger, faulty gas valve), and accidental damage to gas pipes during other works.
How much does it cost to fix a gas leak in London?
The National Gas Emergency Service makes the immediate situation safe at no charge. The cost of repair depends on the cause: loose fitting tightening (£60-100), pipe section replacement (£150-400), gas valve replacement on boiler (£200-500). All gas work must be carried out by a Gas Safe registered engineer.