If they do there is no come back, if they dont then there should be a notice period, but they can still do it.
im no lawyer, but not just a notice period but a period of consultation to gain your agreement, if you agree great, if you dont then when the notice period lapses they can implement the change, if you cant do it then they may have no work for you, but statutory notice periods should probably apply if theres no written contract.
the thing is, if you know it will be implemented and others are going to do it and you cant or wont at best you will gain a month notice of change and consultation, at worst your boss will get rid of you and if less than 2 years wont qualify for unfair dismisal
sound like maybe best to have a chat with your employeer to see if any change can be delayed if you need it or get on board or move on.