Vauxhall Zafira no cranking on key turn

M1 yesterday afternoon, very scary, Zaphira 2.00 diesel club running well, sudden death of power, engine cut out. all lights on the dash on, achieved the hard shoulder thank goodness. no fire, slight smell of hot electrics, engine not cranking on the key. fuses ched and appear to be ok. AA techy couldn't find any problem. Used the diagnostic thing and nothing shown as out of the ordinary, no codes indicated. Oil pressure Ok, Fuel ok, battery up to power, alternator producing well, under bonnet fuses appear OK. bump started and still no fault found. Journey resumed, and motorway speeds were achieved, and got home. still nothing on the key. while running all vehicle lights Ok dashboard light all out except the electronic stability management light, which remained on steady.
(not flashing). where should I look for the problem, what is the problem? help Urgently needed. Thanks to anyone who can help.
Snapper2 M1 yesterday afternoon, very scary, Zaphira 2.00 diesel club running well, sudden death of power, engine cut out. all lights on the dash on, achieved the hard shoulder thank goodness. no fire, slight smell of hot electrics, engine not cranking on the key. fuses ched and appear to be ok. AA techy couldn't find any problem. Used the diagnostic thing and nothing shown as out of the ordinary, no codes indicated. Oil pressure Ok, Fuel ok, battery up to power, alternator producing well, under bonnet fuses appear OK. bump started and still no fault found. Journey resumed, and motorway speeds were achieved, and got home. still nothing on the key. while running all vehicle lights Ok dashboard light all out except the electronic stability management light, which remained on steady.
(not flashing). where should I look for the problem, what is the problem? help Urgently needed. Thanks to anyone who can help.
Snapper2