Gas Safety Certificate (CP12) in London

Landlords in London must arrange a gas safety check every 12 months, and only a Gas Safe registered engineer can complete the inspection and issue the record. The certificate, often called a CP12, must be given to existing tenants within 28 days of the check and to new tenants before they move in. A valid record sits at the centre of rental compliance, because it shows that gas appliances, flues and pipework were checked on time and found safe at the date of inspection. Missing that deadline can lead to a fine of up to £6,000 and, in serious cases, up to 6 months imprisonment.

That duty matters in a city where tenancy changes happen often. London’s population was 8.95 million in mid-2023, and many residents move into the city first before later moving out to other parts of the UK. The rental sector therefore sees frequent re-letting across areas such as Westminster, Hackney, Camden and Kensington, where older terraces and converted flats make up a large part of the stock. A landlord with several units in one block can face different boiler ages, different access arrangements and different certification dates, so a simple annual system saves time and cuts the risk of a missed renewal.

Building fabric also affects gas safety in London in ways that do not always appear on a calendar reminder. The city sits on London Clay, a highly shrinkable soil, and one in 50 houses in London and the South East has suffered from subsidence. Movement can disturb flues, crack seals or affect pipework runs, especially in Victorian and Edwardian homes with shallow foundations in NW, N, W and parts of South East London. Surface water flooding adds another layer of risk, with almost 320,000 properties in London at high risk and one in eight homes in a high-risk zone, so any boiler room, basement cupboard or low-lying service area needs a close inspection after water ingress.

Carbon monoxide is dangerous because you cannot see it, smell it or taste it. A faulty boiler, blocked flue, poor ventilation or incomplete combustion can produce CO, and the symptoms can begin with headaches, dizziness, nausea or confusion before becoming far more serious. Older London homes, especially those built before 1945, can be vulnerable if appliances have been altered, boxed in or left unserviced for too long. Our Gas Safe engineers check for signs that point to combustion problems, flue leakage and unsafe appliance setup.

Since October 2022, landlords must fit a working carbon monoxide alarm in rooms with a fixed combustion appliance, excluding gas cookers. That rule matters in London because the housing stock contains a high share of flats and compact homes, where one appliance may sit close to a sleeping area or a shared hallway. We look at the appliance position, the flue route and the surrounding space, then flag anything that could increase CO risk. If an alarm is missing, poorly sited or not working, the property should not be left to drift until the next annual visit.

Poor maintenance is the common thread behind many CO incidents. Blocked flues, cracked heat exchangers, soot staining and inadequate air supply all point towards unsafe combustion, and those signs can appear in both older terraces in Camden and newer apartments near Canary Wharf. A landlord who keeps gas safety and alarm checks on the same annual rhythm reduces the chance of an emergency call-out later. Tenants also benefit from clear instructions, because they need to know the signs of CO exposure and the steps to take if an alarm sounds.

Our gas safety certificates start from £60, which gives landlords a clear starting point before the booking is confirmed. The final price depends on the number of gas appliances, the access needed to reach them and the amount of time the inspection takes on site. A one-bed flat with a single boiler can be faster to inspect than a house with a boiler, cooker and gas fire, especially where pipework runs through cupboards or behind panels.

London property type affects the amount of work as well. With 54% of households living in flats, maisonettes or apartments, our engineers often work in compact spaces, shared risers and service cupboards, while older houses in Kensington, Camden, Islington and Hackney may have long-established pipework or converted layouts. Homes built before 1919, and the further one in five built between 1919 and 1944, often need extra care around flues, ventilation and appliance positioning. That extra scrutiny is part of the certificate process, not a separate add-on.

Turnaround is straightforward. Once the inspection is complete and the installation passes, we issue the CP12 record and send a copy to the landlord, usually within 24 hours. Keep that record with the tenancy file, then pass a copy to the tenant within 28 days or before a new tenancy starts. If you already have a renewal date on the calendar, booking early is the easiest way to avoid a gap in cover and keep every property in London in line with the annual legal requirement.