OK, you can say that you have worked there for several years and you had had an excellent performance review. Therefore you can say you are an asset to the company and you want to stay there, preferably in the same or a better role.
If they want to change your job, you can ask for the reasons and what the new job specification would look like, together with renumeration and other aspects.
You can say that you will take legal advice upon your options as you do not want to end up in a worse position or have to leave. If you are a member of a trade union you can involve them. If not, you can instruct a UK law firm which deals with employment law to write to your employers if they offer you less favorable terms.
You can also say that you have full employment rights, having been there for years. If they are to go through a redundancy procedure, you need to be properly consulted and all other options considered, for example to be reallocated to different side of the firm. You can ask whether other employees are being similarly affected - if not then ask why not. They have to be careful not to discriminate against you.
Let me know how it goes after the meeting - I will be available later