Update. Had a good look at the car at the weekend. The Distributor has not been replaced which makes me think Steve's guess that the CYL sensor was replaced was spot on!

I've checked the wiring to the distributor and all seems fine there. I also checked the resistance of the both the Crank and TDC sensors, both seem fine whilst the car is not running, but the car stalls if I connect my multimeter when it is running so I'm not able to get a reading. Strange as it does not happen when I do the same test on my own beat!