Pip....Try not to panic.... don't be rushed into going down the early retirement route just because you SSP is running out...as Sarah points out she is claiming ESA at the same time.
Remember that MS is covered under the Disability Discrination Act therefore your employer has a responsibility to make reasonable adjustments when/if you become well enough to return. Remember this could be on a part time basis, or a phased return....or maybe another role depending on what they have available.
I feel awful right now and can't imagine being at work..... but I wouldn't like to think that the option to return in some capacity wasn't open to me.
Sometimes (sadly I think) employers may want the easy/tidy way out so all I would say is think about what you really want to do when you feel better.
I have only been off sick a few weeks, so am not as clued up as Sarah is.... and remember there is a sectin on this site called MS SUPPORT, when you click on that there are sub headings to the left. One section isabout financial support so I would have a good look in there.
I am well impressed by your success Sarah....did you have a confirmed Neurologist's diagnosis at the time of applying for the benefit?