There was no way to share my problem without risking any interesting responses! I am surprised no one mentioned a cold shower!!
I will take the wheel and boss off and check my wiring. Many thanks for all the helpful advice. I also Googled Rachel Riley and she is not the problem....
G
The horn is actuated by earthing the black wire that passes through the hub and connects to the horn push, it is possible to have a short in the horn push itself, you could test the wire by connecting one wire from a test lamp to feed and the other wire to the end of the horn wire at the connector to the horn push. It should not illuminate, if you push/pull the wire and shake the wheel around it should not complete the circuit and the light should stay off, if it does this it points to a faulty horn push, if the light flashes on it points to an intermittent closed circuit (short) in the horn earth wire.
