Good news - just heard that HR are closing the issue. No further action except for me to sign a new contract which doesn't include the shift allowance. Thank you for all your responses - valuable information that thankfully on this occasion I do not need. Been at the company for 12 years now, here's to the next 12!

Pay rise and promotion in Feb 2014 (effective 1st April) which probably highlighted the point to HR. But before that I got a pay rise on 1st June 2010.

I guess because I dont do shifts? But as the contract came after i stopped doing shifts, I thought i was entitled too it. I will look into estoppel more once I know what action the company will take. I'm just trying to keep my job firstly. HR are looking at my contract now, and will let me know through my line manager what the next steps will be and what action they will take. It's either going to be 1) nothing except take the benefit away, 2) take the benefit away and recoup the money, 3) dismissal + recoup the money. If it's dismissal then I will go for unfair dismissal and ulso use the deffence of estoppel if they try and take the money back.

So i knew I was receiving the money, but I did not know it was an overpayment. I thought I was entitled to it because the allowance was in my contract.

OK so i used to work for bank X on a shift pattern for which I received a %age uplift on my base salary. Bank X was bought by Bank Y. Shortly before the takeover I stopped doing shift work and just did 9-5. When i received my new contract from Bank Y, the same %age allowance was included in my remuneration. Because the allowance was included in my new contract I did not think I was being overpaid. My employer has now asked why i didn't tell them I was being overpaid, and I told them i thought it was part of my contract. I understand an employers right to claim back overpaid wages (as long as it was my mistake, i knew I was being overpaid and i haven't spent it), but as it's in my contract would it even been an overpayment? And could they dismiss me? I didn't fraudulently claim, my pay is automatic each month based on my annual salary+benefits. The contract does not define what the shift allowance is for, or when it would start/stop. I just presumed it was a benefit that had to be carried over by Bank Y when they bought bank X. I am primarily worried about loosing my job, but if i do keep my job they may ask me to payback an amount that is equal to about 60% of my annual salary! Please help