Roseclear, the original, was brilliant, but like all fungicides, didn't get rid of blackspot, it controlled it, and only if you sprayed every fortnight without fail. All current treatments do the same, including Roseclear Ultra, but I have read about something new which is said to work.
There's a company called Greenacres Horticultural Supplies, operating on the web as Greenacres Direct. They're based in Iver, Bucks, phone No. is 01895 835235, and they're marketing two products, both of which are aimed at preventing the problem in the first place, and one of which can be applied as a spray for treatment. One is sulphur chips, which is applied to the soil round the roses, the other is Wettable Sulphur, which can be mixed as a spray for the foliage if necessary. Sulphur will make the soil more acid, but its interesting to note that blackspot has become a real problem since the Clean Air Act back in the sixties - prior to that, the pollutant smog containing sulphur particles kept the problem well under control. The acidity will not damage the roses.
That said, roses should be fed, preferably with a specialist rose food, twice a year, once in about April and again 6 weeks later, but not past end of June. Feeding helps them to resist infection.

Thanks, Bamboo - on the button as always! I shall check out Greenacres. We have the least polluted air in Italy up here, according to locals, so that's probably why I've got the problem in the first place!

http://www.armillatox.com/

Gattina, I've just noticed you mention rust and aphids as well - the stuff I told you about only treats for black spot, not rust... might be cheaper to just buy yourself a fungicide spray which treats for both, if you get a lot of rust on your roses. I've never had rust on a rose, black spot's the usual curse.