certifying upgraded fire door

Maintenance

I let a flat in a low-rise building where the freeholder is a local authority. I have been told that I need to upgrade the front entrance door to meet fire safety standards.

The door is a 'notional fire door', so it can be upgraded with the right seals, self-closer and hinges. I can get the work done by a carpentry firm for a reasonable cost.

But the problem is getting the work certified. The freeholder is asking for the work to be done by a firm with 'third party accreditation', and it looks as though this would mean paying for a full replacement of the door and frame at four to five times the cost of upgrading the existing door.

Does anyone have experience of this problem and can anyone advise me on how to get the upgrade work certified without replacing a good front door at considerable cost?