Clean contacts and check fuel pump fuse. Mine would cutout randomly and die instantly similar to failing relay described above. Turned out to be dirty contacts on fuse. Cheap fix

 

Use Deoxit 100 spray the fuse holders and the wires that connect to them behind the CE panel ,
its possible to have a good fuse and a corroded connection behind the panel

 

Just wanted to add an update
after checking every conceivable thing I could on the car I was pretty much settled on pushing it over a cliff. I had checked all the earths at the beginning and in desperation decided to have another deeper look and found that one of the earth wires to the cam cover had broken inside the connector. Soldered it up and not really expecting too much cranked her over and she started straight away. Can’t believe it was that simple after the hours spent on it, bonus is I got some new testing equipment and learnt a lot about my car.
wanted to thank everyone who helped out, this is a great community