Hi Markie,
Just coming back here to update. It cut out again the next day and the RAC ran a diag on it. It pointed to the G28 Engine Speed Sensor. A part what seems to go by at least three names just to confuse the novice even further.
If you google (like I did after getting the results of the diag) G28 and Mk3 Golf the net is littered with people with the same problem.
I have no clue why any and all MK3 forums do not have a Sticky stating if your Mk3 wont start or is intermittent change this plug and play 20 quid part. Hell just change it as you buy your Mk3. Its pean