Rubbish. Several Unis towards the top of the league table for Maths accept students without FM at A level including Leeds, York, Lancaster, Loughborough and Newcastle.
My son didn't do FM (even though his school offered it) and he was accepted into Lancaster (was in top 10 for Maths and not even a RG Uni!) and got offers for Maths degrees from Leeds, York, Loughborough and Newcastle, all of which rank relatively highly. He had three A* in Maths, Physics and Economics! He got a First in Maths and is now working at one of the UK's largest insurance firms. Did him no harm at all!!
Not having FM limited him to which Unis he could apply for, as he didn't want to do the "entrance tests" either, but in the end, he had plenty of choice and got offers from all he applied to!
Obviously, if you want to study Maths at Cambridge, Oxford, StAndrews, Durham etc then you'd need FM, but there are plenty of high ranking Unis that don't require it!
I'd agree with most other posters and say he should progress with a STEM degree which will give him far more options and far greater chance of a more lucrative job/profession. He can use his STEM skills to do specialist journalism or he could even do journalism on a part time or hobby basis alongside a STEM related career or profession which would enable him to use his journalistic talent for something that really interests him rather than just generic reporting on multiple different topics.