Hello thank you for your message.
From the facts you have stated, you have an arguable case before the employment tribunal. Clearly if responsibilities have changed and you were not afforded a private consultation, then your previous job has disappeared. In my opinion you have a right to redundancy package.
The process of starting your claim is to ask your employer for the payment in writing. You must write within six months of the date your employment ends. This applies both to statutory redundancy pay and contractual redundancy pay. If they still don't give you the payment, you can make a claim to an employment tribunal.