Robertson became a barrister in 1973, and was appointed QC in 1988. He became well known after acting as defence counsel in the celebrated English criminal trials of "OZ", "Gay News", the ABC Trial, "The Romans in Britain" (the prosecution brought by Mary Whitehouse), Randle &amp; Pottle, the Brighton bombing and Matrix Churchill. He also defended the artist J. S. G. Boggs from a private prosecution brought by the Bank of England regarding his depictions of British currency.