I'm sorry everyone I should've said right from the start that I construct my tricycles around a kit axle.
To actually go and buy a trike is $$$$$$$ and they are hard to find in the right configuration and frames size 2nd hand - and even then they still tend to cost $$$$$.
With the kit you can use a bicycle frame that you already know fits you and pretty much all the other bits you need (wheels, mudguards & etc) are usually lying in that dusty pile of scavenged bike bits you have in the back of the garage.
My first tricycle - the Raleigh - was built with 20 inch wheels on the back, was singlespeed and had a coaster brake. It did a lot of work for me, but the small wheels on the back brought the pedals too close to the ground and on the rough country roads around here the 20 inch tyres didn't last long.
The Hercules is a big improvement with it's bigger wheels (26inch rear, 28inch front) and its longer wheelbase frame and general robustness make for a much more enjoyable ride. I was pleased too that I was able to use the roadster chaincase with the trike kit which improves chain life and cleanliness; - not to mention the fact that the chaincase no longer gets in the way of easy rear wheel removal. I tried out a SA 3 speed coaster hub on the Hercules, but finally ended up going for the simplicity of a Sach two speed 'Duomatic' coaster hub.