This is an original Lucas Altette, bought from eBay for the Ariel. Apart from one stripped thread and non-original acorn nut, it is perfect.
It came with the right angle bracket, an original Lucas one, that is used on the earlier machines with the smaller battery. Since Amelia should have the big 20 Amphour battery, we will use the straight bracket shown attached to the horn. I bought this from Vintage Bike & it looks like a nice quality part.