Professional indemnity insurance covers a designer or certifier against claims arising from negligent advice, design or certification. Confirm your architect, engineer or surveyor holds it at an adequate level before appointing them.
PI policies are written on a claims-made basis, meaning the policy in force when the claim is made responds, not the one in force when the work was done. If a professional retires and lets cover lapse, their certificates become much less useful.
Ask for the certificate at appointment and note the limit of indemnity and any exclusions, particularly for fire safety, cladding or certification work.