Notice period

[jc1988]

I am a team manager with 14 years service, but I've been offered a new job, I know there was a document floating about with the change in notice period to 13 weeks. I won't be able to give that and feel like it's very unreasonable. Can anyone confirm if it's a contractual change or is it just a Tesco process change and they can't hold me to it? Thanks