on the road bike setting up the gears they work fine in the small chainring at the front, but when in the large chainring at the front and the biggest four cogs of the rear casssette, the bottom jockey wheel does not sit in the chain in want to try and sit on the inside plates of the chain nearest the wheel and hence skips along on the chain. Slight bend in the rear mech hanger???

or any other suggestions?

Have tried 2 mechs with same result

Sounds like it.
Got a mech tool if you’re anywhere near Lewes, East sussex.

Cheers but I’m in Cumbria