You’re right, it’s not available on the NHS, but you can get it on private prescription, it’s about £200 per month from BUPA Home Healthcare, your MS nurse is probably the best person to ask about it. They can probably get you a brochure about it with lots more information, including the incidence of side effects.
There is a risk of seizure, but no drug is completely safe (including coffee and alcohol), so you’ll have to make the choice whether you’re prepared to take the risk and go for it or not.
It doesn’t work for everyone (only about a third of people who try it), you used to get a months’ supply free to see if it works for you - I was on a clinical trial for it, so it was different for me (I’m still taking it, by the way).
This is paraphrased from what the clinical trials nurse has told me:
But as for whether it does make you worse in the longer term - well, it’s the usual problem with MS, it’s so unpredictable, how would you know?
There are lots of other posts on this forum about it if you search for it, it’s quite a regular topic. And all have different views, some good, some bad, concerns about long term effects etc.
As Sue says, not quite a wonder drug though.
Hope this helps, do post again with any other questions.