I have worked for the same company for 17 years.
Two years ago my boss reluctantly agreed that if I could find someone to do part of my job, plus some general other admin type work, I could go part time. I found someone, trained them up over two months, then started working three days a week. Unfortunately that person had to leave after 4 months due to family problems. I found a replacement and went back to full time whilst I trained her up, again about two months. This lady lasted for 6 months before leaving due to a personality clash with the person she HAD to share an office with. Back to me being full time again! A third person was trained up by me. Now after a year she is leaving to do something totally different. I also agreed to work full time if necessary to cover holiday leave for two people in the office and did 3 month full time to cover when one of them was on long term sick. I am paid at standard rate for this ‘overtime’ and get nothing extra for doing it.
If my boss now says enough is enough and I have to go back full time, would he have to make me redundant if I said I would only work part time? I have an ‘amendment to contract’ to show my hours as being 24 per week. ( I actually work 27 but that’s another story).