Is this even legal? I'm not familiar with the UK legal system.
Yep
You basically change the job title and say that the old role is redundant, However, this role is available if you want it... With the three months notice period tacked on.
It's basically laughing in the face of the law that says if a role is made redundant the employer must offer first refusal to the employee on any suitable roles open within the company.
In a nutshell, UK people, your contract means shit.
My old company tried it, I consulted two lawyer, best advice was if its a Company wide initiative then band together and be strong, call their bluff and don't sign onto the new role. I rallied the troops and 5 out of 6 in my dept held their nerve and the company eventually re-wrote our offers of re-employment with 4 weeks notice.
I cannot stress enough reading the fine print of your contract, especially holiday entitlement. Question everything you do not fully understand.