I think the answer is yes. Those of us on DMTS have them prescribed via a special pharmacy. As I was a late arrival for the MS party (over 60) I would not have to pay anyway.
If you have two or more regular prescriptions investigate the season ticket prepayment option.
Yes, as crd has said you would have to pay for gabapentin if you normally pay for prescriptions, and a prepayment may be the way to go if you have regular medication. you can get a 3 month one for about £30 or 12 months for around £108.