My employer has taken on a new member of staff to do my job and changed my job

My employer has taken on a new employee in the leicester area, now i have to work in milton keynes. The employee who had a role in milton keynes left . My hours of work are 8.30 to 17.00 which include travel i now have to start work at 6am and finish at 19.00 .

this has radically changed my job. If i refuse to work in milton keynes and say i want my old role which i was employed to do, can they sack me? 

The role in question pays over 45k when bounuses and overtime are considered i have been in the role over three years.