Audi Q7 TDI 3ltr Oil Leak

[Zoom86]

Morning,
Couple of weeks ago I heard puffs of air and what appears to be oil spitting out of the tappet covers. Delayed getting it seen by a qualified mechanic and shortly after the gearbox malfunction warning message came on the dashboard stating ‘ok to continue but gearbox will have limited functionality’. 

This morning I started the engine which ran for a short while and then stopped and wouldn’t turn back on. Checked the engine bay and found a large amount of oil near the bottom of the engine, some oil under the gearbox and a lot on the engine cover. 
Does anybody know what might have caused this and if there’s anything I could do to get the engine running so I can get it to a garage. 

The car is an Audi Q7 3ltr TDI 13 plate. 

[Bigdave1230]

When you say oil spitting out of the tappet covers do you mean both side of the engine? Did it run and drive ok or was it struggling to idle or seem low on power? Will the car turn over and not start or will it not turn over now? Have you checked the both the coolant level and the oil level? Is there any strange smells coming from the engine bay ie fuel or coolant? How many miles has it done?