Pressurised Crankcase Disco. V8

I left my Disco V8 1992 in Cape Town, practically a write off after a catastrophic bang within the engine which was apparently caused by a pressurised crankcase. The engine suddenly slowed, 'dragged' and then stopped dead. Opening up found a Welsh Plug blown on the oil side which had shed all the sump oil. Has anybody had similar and what was the initrial cause?

crank case pressure is relieved by breather on rocker box,oil pressure blowing blanking plug out is due to poor plug in first place or relief valve sticking,the two things are seperate