ERRATA!!: Following Gary's identification of the problem resistor and my subsequent advice I have looked at the problem again and consulted my own electronics whizz-kid (Merlin). He immediately pointed out that the value of the resistor was incorrect as (using simple Ohms Law) it would have to draw >1.5 amps.
The correct value is in fact 1.5kOhms and the colour code is brown, green, orange. The original problem resistor must have got so hot the the orange band turned brown. Also if the value of the resistor fitted was 150 Ohms it would destroy the Zener diode. Both of these components are available cheaply in Maplins from stock. When buying the resistor go for a 3 watt ceramic type, a few pence more but better for the job and won't fail.
Gary...sorry I didn't get to this earlier mate!
OJ, October 2011