The horn on my Renault Laguna (2001) is continually sounding how do I fix?

My Renault Laguna 1.8 (Sept 2001 model) has suddendly started sounding the horn constantly, the only way I could stop iy was to disconnect the battery.

Does anyone know which fuse supplies the horn? if so what else does the fuse supply? Or ultimately how do I fix it?