Have the method tested that I suggested above. Start the car from the key at the OFF position, let it stall, then attempt to start the engine again without returning to the OFF position. Does it start the second time? From there, return the key to the OFF position and attempt to start again. Does it start the third time?
Also, get the "mechanic" to bridge terminals TE1 and E1 of the data link connector located under the bonnet near the LH strut tower. Read the fault codes(on the dash check engine light), if any and let us know the outcome. I think I have seen this fault before, but I will wait for further information first. Below is a list of fault codes.