Sorry guys, should have updated this earlier.
Had the battery disconnected to check out the steering wheel, but before I could do that, I had to get the car moved to let a delivery through the garage. Reconnected the battery & tried the horn again.
Nothing at first but I could hear a relay clicking so kept the button depressed and after 30 seconds to a minute the horn was back to full voice again.
I'm thinking that the enforced rest the car has had this year led to a sticky relay, which will probably need replaced, but for now at least, I'll try & make the most of the next few days!
Thanks for the input
