OK, bit more checking done, the input voltage getting to the regulators is at +/- 20V mesured on DMM, verified by scope with very little ripple.
The waveforms seem somewhat more defined (attached pics) than before, there is now practically no noticable ripple on the +/- supply rails. I feel there may be some problem to do with frequency stability now rather than interference as if R1 is at its lowest resistance then you get the trace pictured for sine wave, however as soon as you increase R1 value it diminishes to an erratic sawtooth, R6 had to be set rather high to actually get a sine wave which I would have thought should have been somewhere close to its midpoint.