How long before working hours become permanent

[DayShiftWorker]

I was hired on a 4on4off days/nights contract.
To help a colleague, who has health issues. I was asked to work day shifts only. Believing this to be a short term arrangement as no time frame was discussed, I agreed to work days only while he was going through surgery, recovery rehab etc. This has gone on for over 2 years. Can I ask for these hours to remain permanent now that my colleague is coming up for retirement?

You can ask, but they don’t have to agree, even if it’s in your new contract.
We had contract changes at work and were told that, as long as they give you as many weeks notice as yeas that you’ve worked there, it’s perfectly legal and they can make changes to your working days/shifts/notice period to suit the needs of the business.

https://www.acas.org.uk/changing-an-employment-contract/employer-responsibilities