My mother has recently bought a new build flat. The block of 14 flats was signed off in June 2022 by building control.

I noticed the other day that her front door has about an 8mm uniform gap on the door latch edge.  The hinge edge is about 2 to 3mm.  The intumescent strip with brush seal is fitted to the frame and as you'd expect doesn't get close to touching the door latch edge.

The door is an expensive looking veneered redwood door, so adding a lip is not going to be aesthetically acceptable. The frame is a white painted softwood door lining with supplanted door stop and I think is likely to be what is modified.

The company that built the property have an 'odd job' man who has dealt with a number of snagging items to date. When I report the problem I suspect he will come along and rectify it but I'm concerned that it will not be done in a way that keeps the fire resisting integrity of the door frame.

Any advice on what would be an acceptable repair and who I could ask to check the work afterwards would be appreciated.

If the defect is that the closing edge gap is 8mm, then the correct way to rectify the defect is to remove the door assembly or at the very least loosen the door frame closing jamb and reinstall the assembly or pack the closing jamb as necessary to reduce the gap to between 2mm and 4mm.  Then it will be necessary to tighten all fixings maintaining correct gaps and alignment before correctly fire-stopping the gap between the door frame and the supporting wall. Refer to 'BS 8214: 2016 Timber-based Fire Door Assemblies - Code of practice' for support.

If it is a new build, ask the builders to rectify.  If they say there is nothing wrong I would suggest a word with the local fire authority.