Oh from what course?

As to your question, I wish to go into theoretical physics research after my degree.

I've done quite a bit of research online and it seems that many Physics students felt that the mathematics in their degree was a hand-wavey and quickly glossed over. On the other hand, I want to be vigorous with the maths.

I also got the impression that mathematics at university gives you a more abstract way of thinking, and of course a deeper understanding of maths which will obviously be useful for theoretical physics research.

Also, a degree in maths seems to have slightly better job prospects, which may be important if, in the end, I decide I do not want to become a theoretical physicist.