What rights do i have under the discrimination act?

i work a 4 day week my employer wishes me to work a 5 day week (by increasing my hours slightly).this would be detrimental to my health and have doctors letters to prove this,he has now placed me on the ill health register and taken away my protected wage.I am currently on redeployment due to organisational change I have also been told i will be sacked if i do not except a lower banding therefore