Many thanks for the info.
I was offered a 'lesson' in using my new pressure washer by my Pro detailer.
He also supplied me with a foam gun which is the same design as he uses and it is ideal.
Being an engineer and looking closely at the brass body of the many of the foam guns its clear they are all from a similar scource, probably China, and would account for there no manufacturers stamp.
The nozzle and top seem to be of a nylon/graphite material and in regular use seem very serviceable.
The nozzle has a plastic vane which can be adjusted (and because the material is soft) it could be modified to suit the owners specific requirements, further inside will be a mixing chamber which will prove interesting to inspect.
The bottle thread is universal and accepts a huge range of commonly available plastic bottles (try some from the kitchen and see for yourself.
The pressure inlet has a basic thread and this is where the differences occur when a convertor is required to suit various machines (shades of phone chargers here).
Although my foam gun provides a lovely thick layer of foam I will certainly be dismantling the nozzle to see if it can be improved, if nothing else it will satisfy my urge to judge the quality of the moulding and machining and remove any flashes that may detach themselves and cause damage at sometime in the future.
Obviously foam is a blend of air, water and a chemical but Im inclined to think of the foam gun as a fancy cocktail shaker and as in mixing cocktails the slightest change in any one component can produce a complete disaster or a absolute triumph.
Happy cleaning