Ok, from reading that, I would say you have two things going on in your tank at once. For this reason, please tell us your exact water stats (i like to see numbers, not they are "ok" because i have had people tell me they are fine when they are not).
First of all, it sounds like you have a bacterial infection going on in the tank. The ulcer, fin rot, and swim bladder problems (loss of balance) are all symptoms of this. I am not familiar with the UK meds, so listen to Wilder's advice on that, she knows them very well.
Secondly, it sounds like you have a parasite infestation going on as well. Fish flashing is usually one of the big signs, and since you can't see them, my guess is either gill flukes or skin flukes. Both are common parasites. They seem to have infected the gills of the fish judging by the color (pale gills as well as red, inflamed gills can be a sign of parasites. Again, listen to Wilder on this. She knows her UK meds very well.
As for the lumps, i have no clue. However, lets look at it this way. There are three treatable categories of fish illnesses. Bacterial, parasitic, and fungal. True fungal infections are rare, and I do not believe you are dealing with one. That leaves parasitic and bacterial. You already will be treating both of those, so hopefully the lumps resolve themselves while treating the other illnesses.
Ok, water stats look good, so they are definately flashing from parasites, not poor water quality.