I finally worked out how to control the dramatic swerving from one side to the other as I tried to control the takeoff roll down the runway.  It seems I was not getting off the ground quick enough i.e. as soon as I reach 85mph.  Below that speed the tendency to swerve is much less and just about controllable with the rudder. Hope that's of help to anyone else who's been struggling to get t clean takeoff.   Sq.