Am I not justified in being miffed at working hard for a £1500 p.a. payrise, then getting £1750 taken off me in extra tax?
No you are not justified in being miffed IMO.
You had the choice of leaving school and going straight into work, but chose to further yourself by getting a degree. You knew the loan repayment terms when you started and you now need to live by your earlier decision.
Look around you and you may notice that a lot of people are losing their jobs rather then being awarded pay rises.
You may have been to University and obtained a degree but you still seem very capable of acting like a spoilt child.