I was promised an extra £1,000 if I switched to a different job in the firm. I asked for the salary increase in writing, but the manager just said I’d have to take her word for it. However they’ve now gone back on this, and they won’t let me return to my old job where I was earning bonuses of up to £150 a month.
If you have any evidence that you were offered the £1,000 you could take the firm to an employment tribunal. However if you don’t I suggest you use the firm’s dispute resolution procedure. Make sure everything’s in writing, and put it to your manager that, since the increase didn’t materialise, there was no change to your employment contract and you intend to resume your old job. If you can’t resolve this see a solicitor specialising in employment matters.