155 snag....possibly seized engine?

[silverback mike]

Hi folks,
Pottering along the M5 night before last the 155 developed a cough, injector light came on, started spluttering then stalled.

Initially on trying to restart it spluttered, then nothing....

Turn the key, not even an attempt at a turn.

So I had it recovered, they have diagnosed a seized engine.

I initially thought it was a coil pack but obviously not now.

Any ideas?

Also, the engine doesn't turn when rocking it in gear. so can't be starter motor....oh, and haven't been able to check cambelt either.