Thanks for all the inputs and ideas guys.
In the end the remarkably simple solution was - tyre pressures.
Took the van out and went via Sainsbury's to check the pressures. Mrs Moncman had found a few posts on forums reporting similar crap handling due to under inflated tyres. In many cases with new vans that had been through PDI. I picked mine up 3 weeks before our trip to France and didn't have time for a practise run out. Dealer signed the PDI with ticks in all the boxes included tyre pressures - 65psi. Found out today they were at 54.
Anyway - towing like a dream now even with the bikes back on and little internal ballast. The van is naturally nose heavy probably owing to all the fancy kit under the front bunks - motor mover module, wet central heating, alarm, on board water tank etc etc. Putting stuff aft of the axle is the only way of getting the nose weight the right side of 100kgs.
Anyway thanks again. I've added a pic of the rig from this evenings run.
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