Can homeworking be turned down if I did it before?

I am due to be back to work after 12 month maternity leave. On my return I have requested to work from home and to be working three days for the period of five months and ramp up to be full time again. There was no maternity cover in place for my post. I believe this is due to re-structure that has taken place whilst I was on maternity leave whereby other people have taken on my responsibilities in two new departments. Prior to my maternity leave I requested to work from home which was granted for the two months before my maternity leave. In my flexible working meeting, it was implied that working from home will be difficult, but I was encouraged to write a letter. I mentioned that there is another person in the company, a man, with the same job title who is based from home and his work never suffers. I was then told this is an exceptional and historic contract that would never be granted currently. The company is undergoing a lot of changes currently and I am aware that my responsibilities have been outsourced to new employees outside of my current department. My worry is that they will refuse flexible working request,  forcing me to resign. Can they do this?