Update.
ECU damaged. Approx £800 to fix!

There should be a warning on the battery cover to never use jump leads.
 
Second hand ecu programmed with
Testbook
Faultmate
Or IDS JLR
Perhaps
 
I guess the best/safest way to do it if you are really stuck is to connect the two cars via jump leads, leave the running car ticking over for 20 or 30 minutes to put some charge in the dead battery then disconnect the leads before trying to start the dead car. I've never had much luck jump starting cars anyway without letting the dead battery charge for a while.

I always do it this way then no problems should occur.
 
I've got slave batteries in my hippo commercial, so can jump off them & they can be separated from the vehicle electrics, I also have my jump pack, which is my preferred method, especially as it's not always possible to get close enough to the other vehicle.

A good jump pack will get most engines started, but I will always say to go with the most powerful you can afford... I use a Snap-On 1700ca 12v pack & it's never failed to start a vehicle, whether 1ltr petrol or a 6.5ltr diesel v8 with totally flat batteries. A lot you get from Halfords etc are quite low, but don't get anything under 800ca, even then, I've used company ones (Clarke etc), which have struggled to start a transit.
 

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