For anyone interested in retrofitting a multispeed hub to a brommie, there are two UK shops I know of:

Kinetics ? Recumbents, Folding Bikes, Custom Bicycles | Brompton

About Tiller Cycles

...although the fellow from Tiller Cycles has scaled back quite a bit. If memory serves, he was operating a business from a houseboat and got all kinds of flak from the authorities for doing so.