Embarrassingly , I`ve discovered that the fault was simply due to to a
sticking/ faulty brush!
When I tested it using a meter , all the prodding and poking must have given me
the reading OK, but it must have been an intermittent/poor contact with the
commutator as it wouldn`t work when switched on from the mains.
What puzzled me originally was I hadn`t smelt any burning etc.( and so had my
doubts about burning out the motor) and everytime I tested various parts , I
obtained OK readings .This sort of defied normal logic. This, then made me
think that perhaps there was an intermittent connection so I dismantled the
brushes and one of them was fairly stiff in it`s holder.
I cleaned them both up( and the comm ) and refitted them and now all is OK.
I knew that using a digital meter could lead you to the wrong conclusion
sometimes so I was surprised that I was led astray using my old analogue
Thanks for all the advice