Where do I go from here?

Hi, I get paid an annual bonus. This was paid last year, despite no KPIs in place, without question. This year I am told that I will not be paid as I did not meet a certain criteria - this was never discussed and is not something I can rectify as this is for last year's performance. I am very unhappy about this, but have been advised to try and negotiate for part payment. My contract states 'You will be paid an annual bonus of £xxxx'. Nothing more - what do I do now?

If your contract literally just says you will be paid £xxx and doesn't say anything about it being dependent on criteria, then you are owed it as part of your contractual remuneration, the same as your salary. Difficult to see why it's called a bonus if you are literally guaranteed it every year, but if that's what your contract say, then that's fine.

Write to your employer quoting your contract and pointing out that payment of your bonus is not dependent on any criteria, so failure to pay it as per your contract would be breach of contract.