Hi Simon,
The bonnet switch was changed as I had a new one and the slam panel was off at the time.
Yes there a 3 horns 2 on the slam panel and 1 under the plenum splash shield. With the fuse removed horn buttons are inoperative and if I lock the car with the bonnet open I can hear the toot coming from the plenum distinctly. Also I have removed the plenum cover and seen the horn many times.
My car does not have a BBUS. Have just replaced the battery as suggested, one I removed was 12.5V replacement is 12.8V and within 3 mns of replacing horn fuse, twin horns constantly sounding again. I can only assume it's the relay as everything else on the car is working perfectly. I have a FBH but the BUS wire has been cut as suggested by Trebor and if it's not the relay I'm out of ideas at this point.
Lee.