Firstly, people don't get made redundant, roles do. So the fact that your previous role is gone could mean that a redundancy situation does exist.
Your employer is trying to redeploy you which is to their credit. You're refusing to take up that role so they could argue that you've actually resigned and are not being made redundant, especially if they were prepared to put an effort into training and upskilling you so you would be suitable in the long term for the role.
As you have between 10 and 15 years service they are obliged to give you 6 weeks notice. As you have not been given anything in writing, they have not given you notice and that notice period only starts when they give it to you in writing. if you exit the company before that period is up (which is very common), they are required to pay you Pay in lieu of Notice (PILON Payment) which is taxable as if it were your normal wage. In effect, if you exit 4 weeks early, they pay you your wages for those weeks
They have no obligation to pay you any more then your statutory redundancy, although if they have a redundancy policy that says different or a precedent for ex gratia payment has been made in the past, I'd be asking why are you and your colleagues only getting statutory