Have taken all the advice - taken the weight of my arm/elbow and wrist - reduced typing dramatically and symptoms have almost disappeared - just a slight 'prickle' comes back if I type on my notebook for any prolonged time however...
Hopefully acceptable resting and revised care of my arm posture will cure the problem in the longer term - see how long it takes to go completely
As above comments from DocM and a few others previous I have been not supporting my arm and/or bending my wrist back when typing or resting on the desk