Beezo, if you want, or need, to use a Renault dealership then go for Renault Trucks over the Renault Car dealerships any day.
They are relatively expensive at £55 an hour plus vat but they know their stuff and good customer service.
There are two Thompson Commercial dealerships up your way, one at Billingham and one in Newcastle.
Be aware that if the MH is under warranty that Renault Trucks and Renault Car dealerships cannot do each others warranty work. You need to ascertain which bit of Renault supplied the base vehicle originally as they cover the warranty.