Upon a change of shift patterns within the company I opted to swap my preferred shift with my work partner due to  her having a young baby and she would not of been able to work the hours offered.  This was on the understanding that when a vacancy came about i would be able to take up the option on my preferred shift.  This was put in writing with personnel.  Since then I have been diagnosed with Bowel cancer and a new manager has been appointed.  All my doctors that I am under consider it would be beneficial for my health  to be transferred to my preffered shift because it involves only working three nights instead of four on the same pay.  The company has two letters stating this from the consultants treating me.   Since being off sick the new manager has taken on a new person and has promised her the same shift when it becomes vacant that I wish to transfer to.  She is quite openly going around telling people that she  is only working four nights temporarily till i come back and  then she will  be transferred to three nights.  She is on a temporary contract as well but the manager is fighting for it to be made pernament.

Whilst I do not consider the company should create a new position for me but as we are both under the same  manager and it would involve him breaking his word to  the new person can people please advise what my situation and rights are.