My horn is not working and I have checked the fuses and it is not this. The problem is I cannot find the horn under the bonnet to check that! It may seem a bit of a stupid question but I have been looking for ages. Can you help?

The horns usually aren't in clear view. More likely tucked inside the fender or behind the headlamps.
Try looking up behind the front bumper on either side of your car. Have an assistant hit the horn button while you search: it may click slightly with each push, thus making it easier to locate.
Good luck. I hope this helps