Changing employment contract advice UK

Hi all

I work for a large company in England for over two years now which is going through an internal merger (my business unit is merging into another one). My line manager spoke to me on Zoom last week telling me that my role & contract needs to be aligned to the new structure and I’ve been offered two alternative positions within my team. Now this is where the issue is. One of the roles offered is doing what I’m currently doing but on less pay and the other one is the same pay but a ‘junior’ position doing something a little different. In addition, both of these roles have a ‘variable base’ as the work location and my current contract is ‘home based’. I’m not happy with either of these options because they are a demotion in one way or the other and I also do not want to change my contracted work location. I don’t have a copy of my contract at hand (plan to get this on Monday) but would appreciate any advice on what I should do.