What is a landlord certificate?

There is no single document called a landlord certificate. It is a catch all for the safety records you have to hold and renew on a property you let.

In England that usually means a gas safety record if there is a gas appliance, an electrical installation condition report, and an energy performance certificate. Depending on the property you may also need a licence from the council.

They renew on different clocks, which is the whole problem. Gas is annual, electrical is every five years, an EPC lasts ten. Miss one and the penalty is not proportional to how small the job was.