What it is
A statutory document from your Building Control body confirming that the work, as inspected, complies with the Regulations in force at the time.
What it is not
It is not a warranty, not a guarantee, and not a comment on workmanship. It is also not the only paperwork you need — competent-persons certificates for windows, gas, electrics and ventilation sit alongside it.
Getting it issued
Final inspection, any outstanding non-conformities cleared, and the relevant trade certificates submitted. Until the certificate is in your hand, the project is not finished — regardless of what the keys say.
Frequently asked
You can usually progress it directly with the Building Control body. Take advice early — the route depends on what is outstanding.