Done it
Ok folks, Smoked 3rd brake light is a success
I bought a piece of 7" x 16" charcoal film from
www.lamin-x.com they do a light smoke and a dark smoke, I had to email them after placing the order to request the DARK smoke. There is enough film for 3 attempts
My first attempt wasn't very good

Reason 1, at the bottom of the lens there is some raised letters and in the center there is a raised symbol. When the film was stuck over these it left raised areas which looked bumpy and horrible

Reason 2, the end of the lens goes very narrow, as a result, when you pull the film over the end it all gathers up excessively. I warmed it with (rakeys

) hair dryer but it wouldn't mould itself properly around the edge
So after an inquiry form a fellow MINI2 person who wondered if I'd completed it, attempt No2 was just made.
First the raised letters were trimmed with a stanley knife and then rubbed down with a fine wet-and-dry paper, used wet. The finest I had was 400 which left scratch marks on the lens, 1200 or 2000 would have been better.
So my now finely scratched lens

was polished with a car polish to reduce the scratching. Then the lens was cleaned with 50/50 alcohol (no not the drinking type

) and water.
A new piece of film was cut and the lens placed on top. A heat gun was then used to warm the film and it was pulled and stretched over the ends and sides. The excess was then removed with a stanley knife.
I'll fit it tomorrow to The Weasel after I've washed it and take some pics of it in place.
For now though, here's some pics of it on the table and one pic of my first attempt
