The landlord gas safety certificate, done on time and issued the same day

The CP12 is a record of an inspection, not a guarantee. It lists every gas appliance in the property, the checks made on each, the results, any defects found and what was done about them, and the engineer's registration number. It is valid for twelve months from the date of inspection, and a renewal can be done up to two months before the expiry date without losing any of the remaining time, which is how a sensible landlord keeps the anniversary in a convenient month.

For each appliance: the gas rate and burner pressure, the flue and its terminal, the ventilation, the flame picture and, where the appliance allows it, a flue gas analysis for combustion performance. The flame supervision device is tested, the case seals are checked on room-sealed boilers, and the appliance is confirmed as safe to use, at risk, or immediately dangerous, using the industry's standard classification. For the installation as a whole: a gas tightness test at the meter, the condition and support of visible pipework, and the emergency control valve.

What it does not cover: the appliances the landlord does not own. A tenant's own gas cooker is not the landlord's responsibility to certify, although the pipework and bayonet fitting that serve it are, and most engineers will check it if asked.

In summary: an annual check by a registered engineer, a copy to existing tenants within 28 days, a copy to new tenants before they move in (and, for a section 21 notice to be valid, before the tenancy starts), records kept for two years, and any defect that makes an appliance unsafe dealt with before it is used again. Landlords of HMOs and agents managing on behalf of landlords carry the same duty. Where a tenant refuses access, the landlord has to show reasonable steps were taken, which is why access attempts and refusals are recorded and passed back to you in writing.

Only an engineer on the Gas Safe Register may carry out this inspection, and the register is the only way to check. Every engineer carries an ID card with a photograph, a registration number and the appliance categories they are qualified for on the back. Tenants are encouraged to ask to see it, and the registration number is on the certificate for you to verify at the register's website.

Twelve months from the inspection date. Book the renewal in the two-month window before expiry and the new certificate carries the original anniversary, so nothing is lost by being early. For a portfolio, the sensible approach is to bring all the anniversaries into the same month or two and inspect the properties in a run, which is quicker and cheaper than one a week all year. That can be set up from the first visit.

The price depends on the number of appliances and whether a boiler service is added, and it is agreed in writing when the visit is booked. Multi-property bookings are priced per property with the travel between them taken into account. There is no charge for the certificate itself; the price is for the inspection, and the document is part of it. If a defect is found, the repair is quoted separately and you decide.

Give the address, the tenant's contact details, the number and type of appliances and whether a service is wanted. The engineer arranges a time with the tenant, attends, inspects, and emails the certificate to you (and to the tenant, or to the agent, as you prefer) the same day. If the tenant is not in, a card is left, you are told, and a second attempt is made without argument. If an appliance is found unsafe, it is disconnected with the tenant's agreement and labelled, you are called immediately, and a repair or replacement is quoted.

Single flats, HMOs, whole houses, blocks with a boiler in every flat, and buildings with communal heating where each flat still has a gas hob. Studios above shops, basement conversions, and the occasional property with a gas fire nobody has used in a decade that still has to be checked or capped. All across London and the surrounding towns.