The op does say he has no flashing lights/warning lights so no codes will be stored if i am correct

Apart from "vehicle fault shutting down" as mentioned by the OP.
Many faults are stored without any warning lights or messages being displayed. 2008 MY Java Black TDV8 HSE

But it does not shut down and goes back to normal after a bit so would suggest either a battery but op has tested it or a loose connection some where which would come up with a u code lost comms with what ever

Have ordered a new battery and also booked in on Monday for mot..service and to check fault codes.Hopefully will be able to get to the bottom of it. Thanks for all advice. Will post when they find out the problem.

Finally got sorted...it was the instrument cluster causing all the problems. Took so long because warrenty wanted the garage to go through lots of hoops before they would order new cluster. My thanks to Jagtechnic of Eastbourne for their perserverance and patience.