It is rare that the cause of swim bladder problems are actually because the problem is in the bladder itself. Rather swim bladder problems are usually a symptom of another underlying problem.
This can be a bacterial infection, a parasitic issue or a constipation issue. My normal assumption without any better evidence is that the cause is most likely constipation related. Plugging the fish ends up putting pressure on the bladder. If this is the case there will be a few clues. One the fish will not be pooping, two the fish may be swollen and, three, eventually the fish will stop eating.
If I am convinced constipation is definitely not the cause or I have used some Epsom salt or been able to feed laxative foods such as peas or daphnia and the fish has begun to poop again, then I will look to a bacterial cause if the problem persists. In this case antibiotic treatment would be the solution. When I have no idea what bacteria may be causing the issue, I would use a broad spectrum antibiotic to treat. If the fish is eating, medicated food will normally work better than water dosing and is cheaper too. One can often buy antibiotic containing food or else make it oneself.
Unless a fish is wild caught, I tend to look to parasites or worms as the least likely cause and will only treat for that if the I have ruled out constipation and bacterial infection as the potential causes. Fior that there are several tretments which range from metronidazole to praziquantel to dewormers such as flubendazole or levamisole.
However, these meds are all easily obtained in the USA where i am and you may have difficulty finding things in the UK. Hopefully some of the many Brits here can help with that.
I hope this helps some.