ok, so finally got around to this job weekend just gone. Bumper was easy to remove, seeing as there were only 2 screws and 2 bolts. Popped that off and my horns were under the passenger side headlight.
The bracket the horns mount to is nut and bolted to the body and everything on it was corroded. Pop the whole thing off, cleaned everything up (including emptying a load or crap out of one of the horns), gave the terminals on the horn a clean on my spinning wire wheel, bolted it back together and job's a good en!
All in all I would say it took about 25 minutes and the fix was free, which is even better.
And with the spare time I had left over, I rewired my aftermarket headunit, so that even works properly now and took the opportunity to fit my Parrot MKi9200 bluetooth kit as well, all in all, it was an hour well spent.
Thanks again for your help