Hi, Mrswoman,
Was very briefly in the Cambridge County Record Office today, so had a look in Spalding's Directory of Cambridge for 1935/6 under Opticians. There were 14 names listed there, but unfortunately not your HAYES man. The nearest entry was HYMANS and COX at 7, St Andrews St.
Couldn't find him back to 1930, nor up to 1937...
Very best wishes,
keith