I forgot to say that the LED will not turn fully off when the 74HC595 output is high, I've connected the base of the BC337 via a 1k resistor
What is the rest of the circuit?
The BC337 is an NPN transistor so the emitter should go to ground with the load in the collector to the +ve.
It was as you say with a 1k res on between the base and the 75HC595?
Measuring the ADJ pin when the lamp is on I get 5.5V, as fungus said I have tried the ADJ pin connected directly to the 74HC595 and it seems to work nicely, I'll just have to figure out how to invert it in software now
the only thing is it doesnt turn fully off, very nearly and hardly noticeable. Would a resistor between the ADJ pin and GND help to pull it low when the 74HC595 pin is not high?