I recently had a fire door inspection at my flat, and my door failed due to excessive gaps. I wasn’t fully convinced, so I purchased a fire door gap gauge to check myself.

The measurements I took show:

• Hinge side: gap is only 3mm — well within the acceptable range (2–4mm).

• Lock side: from around the lock down to the bottom, the gap increases to 7–8mm.

• The rest of the door is within limits.

💬 My question: Can I fit a fire-rated door lipping to the edge (lock side) to reduce that gap?
My door thickness is 44mm (standard FD30).
The contractor quoted me £1,500 for a full replacement, which feels excessive when only one section is affected.

Has anyone else done this or had success with a certified repair?

More worrying that the 'inspector' failed to comment about the disconnected self-closer!!!  That's far more serious than an excessive door to frame gap. 

The gap issue can usually be best rectified by adjustment of the door frame jamb. But subject to survey, lipping replacement might be possible.