Fixed.
After a good strip down, clean and some grease I reattached the nozzle to the lance.
Stuck fast in one position, would not turn to change jet type.
So last resort, two towels to aid purchase, gripping the lance in one hand and the nozzle in the other and counter twisting......my it's stiff...keep trying....click... whatever was obstructing the turning mechanism must have snapped back into place and the nozzle now turns as it should. A great deal of force was needed, a bit like opening one of the curry sauce jars Mrs. C insists on buying.