that makes the relay pull in very susceptible to variation in mains supply voltage.
a 1W resistor should be adequate
I saw my use of the zener to be (while reverse-biased) holding the relay coil at 12V. It then becomes the catch diode for back-EMF (while forward-biased). It does double duty.sofaspud, that would defeat the purpose of the catch diode, which is to prevent relay coil back-EMF destroying Q5.