Streaks on body and fins is almost always a sign of bacterial infection. A good antibiotic is the best way to treat this, but you can only get these from a vet in UK ("sigh").
Quinine Sulphate might be beneficial, and this is found in some brand name fish meds - like some of the Sera range, and I know for a fact that it is in "King British WS3".
Because its goldfish (and I dont know much about coldwater fish health) you might find feeding with a medicated food helps. Two I know of are Medi-Gold & Metromed (but again, not sure if these are available in UK)
As for the yellow lumps... they could be a fish louse. Look very very closely and you should be able to see two dark dots (these are its eyes!); if its a louse. If so, you can pull it off using tweesers I think - but again, I would do a bit of research on this as I have never treated for fish lice myself.