London recumbents very kindly made me aware of Nihola who produce these trikes which can be had in either a load carrying form or an advertising poster form as pictured. The advertising form has the option of an opening front thus providing space for your promotional gifts, lunch, beer etc. They come with 5 or 7 speed gears and front drum brakes. They'll carry 100kg and have an unladen weight of around 33kg though this obviously depends on which of the huge range of options and extras you choose.
This Cambridge firm supply Winther's Kangaroo model (third pic down) which is primarily designed for carrying kids but could be used for shopping or packages.
Despite being in holland Dutchbike.co.uk
will import their cargo trike (bottom pic) direct to your door but crucially
they seem to have established a network of people and dealers in the UK who would give a test ride. One correspondent told me they had lent him a bike (2 wheeled bakfiets) to try before he decided to buy. He's promised me a road test report in the new year.