Don't see why it would be anything other than useful!

fit the fire doors for the building control and then put the old ones back later, everyones happy.

Some years ago Itook 6 (4 inch thick) doors to a timber yarg with a Big Band saw sliced them in 2 adding an approved 30 min. aspestolux (in those days) pannel and then sandwitching it all back together.
They took a lot of making good where the pannels tapered and we trashed one door before getting, but it worked in the end.
The trick is a very big band saw and move the job through very slowly.

But I dont think that I would want to try it again.

No self closers means no need for people to wedge them open!

The point being that there is no law forcing all these fire doors to be closed, therefore rendering them useless as fire prrotection when open.

Smoke alarms are mandatory and very sensitive, one might think those and a fireblanket or two might suffice?

Tearing my hair out! Having to replace beautiful oak doors with FD30's. Both common sense (not so common these days) and logic are now out the compliant window, as it were!!
New FD30's with self closures can't be opened by our children! Building Control will not comment.
Mains coupled Smoke & Heat detectors in EVERY room is not an acceptable solution to Building Control. Their comment is that if they are to fail then the FD30's would save the day. They would save the day for Building Regulation Compliance but not the lives of our kids who cant open them. Should 8 detectors go off sumultaneously the whole town would splill in to the streets - and nobody in the house is likely to hang around for half an hour.
Rumour has it that some councils are accepting the "coupled alarm system in every room" solution as an alternative to FD30's.

Some years ago,i converted a Victorian house to flats and was told all the doors had to go and be replaced with hideous fire doors.The customer wasn't happy but BC wouldn't budge.When i started the job,one of the first tasks was to put oil tempered hardboard on upstairs floors and seal round with firefroof sealant.Tracking down said sealant led me to a local joinery manufacturer and supplier.I got chatting with him and he asked me what i was doing.When i told him he said that he was in fact an expert on fire resistance and regularly gave talks to local BCO's.He also said that there was no need to remove the lovely old doors because he had the products to fireproof them and that obviously the BCO i had been dealing with hadn't taken any notice at the frequent seminars he had given on this very subject.He asked me for the BCO's name,said he knew of him and would ring him and put him straight.This he did in my presence and i had no more trouble after that.The guy came to the house with me,showed me all the steps i had to take and supplied all the materials,boards,sealants,paint,door closers and intumescent strips.Obviously he got a lot of business from me but it taught me a lesson.Building control don't know what they are doing a lot of the time.

I'm a newbie BTW.