I'm not male, but if I were you, I'd definitely go and get properly measured for a suit.
If you can, I recommend you spend a bit on it, actually. You'll be able to use it whenever you need to be a bit formal, and nothing gives confidence and a good impression like a well-fitting suit. Don't buy things that have specific sizing like suits on the internet unless you are sure of what size you are, it's a pain to return things ordered online.
The sales are on at the moment, I've seen £400 suits selling for £175. Moss Bros or T.M. Lewin are good High St. suit stockists. Have a look and see. Marks and Spencer should be good at this too.