Is UK QTS a global status or is it per-subject? I am considering taking a PGCE course to get myself QTS.
The only PGCE offered in the area, however, is Mathematics.
While I am sure I can teach Maths, I'd rather eventually teach softer subjects.
Upon attaining my QTS, will I only hold that status for teaching Maths, or for teaching in general?
This is what the Target Jobs website (first result on Google, I'm sure there are other sources) has to say: 


  Once you have achieved QTS, it's legal for you to teach any age range, although it's not easy to move from one to another. 


They also say that if you specialise in primary school teaching (ages 5-11) you would be expected to teach every part of the National Curriculum (i.e. everything from Maths to Modern Languages, Physical Education and Art).

If you specialise in secondary school teaching (ages 11 upwards), here what Target Jobs says:


  Initial teacher training in secondary teaching entails a specialist subject, but once you've gained QTS, you're legally qualified to teach any subject. It's common to find teachers in schools teaching subjects other than those they specialised in during their teacher training.


So it seems that if you qualify as a maths teacher in secondary teaching you can easily change subjects. However, it's much harder to change age ranges once you have specialised.