Having been working on the car since Snetterton, fixed the electrical gremlin - bad earth on the cut-off switch, the base plate has to make a good contact with the chassis so it can cut +ve and -ve connections. There was 10 ohms resistance between the plate and ground, when you try and draw 100+ Amps to start the engine it cuts off. - works fine now.
checked out the oil leak, and possible turbo failure, it appears that the temp sensor got blown out of the oil filter housing, leaving a 10mm hole, found the sensor hanging down still attached to the wire, it must have been getting soaked by the oil flow and it was still reading 130+ °C. The small valve in the oil filter housing must have closed and kept the oil in the engine rather than pumping it to the oil cooler at the front of the car as there was only approx 2 litres of oil left... (normally 6 litres) and the switch in the sump which is usually used to warn of low oil levels cut off the turbo so it survived.
Did some basic tests on it and it appears to be providing reasonable levels of boost / suck on the intake. Tested by unplugging turbo, ran engine to 5000 rpm, tested the suck - reasonable, then did the same with the turbo connected - nearly ripped my hand off...
Going to take it to Andy's at Greenbrook Garage on Friday for a proper check over... have got a spare turbo so can change it if required.