Stef, I'm glad you seem to have figured it out. Mine had almost exactly the same symptoms for almost a year. In the process of sorting it out I replaced the dizzy cap, rotor, leads, plugs, battery, fuel filters, fuel pressure regulator. I checked the injectors and cleaned out the petrol tanks. I tested with a different Dicktator module and ECU, and still it cut out. When I had done all I can, Louis took over. He could see on the computer that there was a voltage problem, but we still couldn't figure out where exactly. The last thing we did was to replace the alternator charging wire and go through all the connections in the loom. I couldn't see any problems with the connections, but it could be that just manipulating the wires fixed whatever was loose. The alternator charging cable was definitely dodgy, so it's more likely that was the problem (although it still cut out with a new, fully charged battery, so I don't know).
The trouble with these kinds of issues it that each time you think you've solved the problem. Then 50km later it does it again and you're back to square one! Luckily I've now done about 5000km without a hiccup, so hopefully it's now a problem of the past! Also, just about everything else is new so I should have many trouble-free miles ahead