RAMDOM STOPPING OF ENGINE

Hi,
I have a RR Sport Autobiography 2011 petrol,
Recently it has been stopping at random times, starts right away then may run for days or will stop 15 times a day.
Took it into Beadles Sidcup/Swanley who changed fuel filter etc then did various checks while they had my car for over 5 weeks, Yes thats right.
Still no idea what's wrong???
I get either:
Restricted performance/key not found??
Have had new petrol pump fitted and thought it may be the throttle body but nothing found.
Causing real concern as when engine stops i have no power steering and is getting dangerous to use.
Have spent a small fortune on this and no luck, Written to JLR but the only responce from them was " well its an old car" Christ its not 10 yrs old.
Bad enough as i had to have all the power steering pipes changed as they just rotted away and this is all i need considering this car cost an absolute fortune new.
Any help would be appreciated and a financial reward to the genius who solves it for me is waiting.

Regards.
Tony

Sadly sounds like a corrosion issue in the ECM or Body Control unit. I am betting either the sunroof has leaked or the drains have backed up causing water to get into the control units. If I recall correctly on the RR they are in the back on one of the sides and get wet you will have lots of issues.