Disco 1 D1 V8 running rough when warm

Hello All the guru's,

My very late model D1 V8 is OK when I start it up but when I have driven it for around 4-5 miles it starts to run rough and smells rich from exhaust.
I have had my ECU mate on and there is a huge imbalance readings on the Lambda sensors, bank 2 reading is very high and bank 1 reading OK.
diagnostic reading signal from ECU lost.
I would just like some confirmation Lambda is problem or could it be ECU, I suspect the lambda as surely the ECU would show fault from start up
Any help and input appreciated
I have read lots of posts on this issue running rough when hot but just makes me more confused.

Cheers Ian

The V8 runs a lot better on LPG but still flashes up EML when running low revs

Ian