MI5 would not be involved in extranational operations. That falls under the purview of MI6.
Special Consul Bakshi claimed the interior of his car was Iranian diplomatic territory, that Adam was "now in Iran".
This is completely false.
The driver of the car may claim diplomatic immunity for driving or parking offences, but that is the limit of Diplomatic Vehicle immunity.
In tests, in the US, only 3 out of 50 vehicles were stopped by an EMP, and two of those were successfully restarted, and seeing as the Land Rovers used were diesel engined, the EMP would most likely not affect them.