Have you considered a big pickup with the crew cab option? Walked past local Mitsubishi stealers this morning and they had some beast or other that said it had a 3 1/2 ton towing capacity. Should be ok for a pikey wagon.
I bet though it would not meet Mr Entwood's objective of being heavier than what he wants to tow though, he wants something heavy and suspect UK pickup's would not fit the bill.
My Ranger had a kerb weight of 1,968 kg and towed a lot more weight than Entwood's pikey palace* quite happily up the motorway between Bracknell & Northampton
Of course, it's Diesel and there'll be a long string of reasons it doesn't fit the bill
but I loved mine - fantastic car and I'd have one again in a heartbeat.
*Probably. We had a car trailer loaded up with the Cobra (incl. engine & gearbox)
and the contents of my garage packed in around it! Didn't weigh it, but it can't have been light.