If you’re in Stafford then I’ve used the Arnold Clarks branch there (I use it as a staging post on trips to london and swap vehicles there from time to time – do the miles from scotland in a berlingo, do the work in london in a luton and swap back on the way home) their van fleet are typically pretty new and in good nick – never had anything from them with more than 30k on the clock and often less than 3k. All their vans have proper bulkheads and the load spaces are ply lined and should be nice and clean inside, front and back. For a long hire you should be able to negotiate a decent rate – usually 7 days for the price of 4 or 5.
Over those distances you’ll possibly notice fuel consumption a bit in a tranny relative to a car, so if you’ll normally manage with a galaxy size down to something like a Scudo, to be honest I don’t see why a berlingo wouldn’t fit the bill and you ought to be able to get one of them for around £15 – £20 a day over that duration. Typically with hire co’s you book a class / size of van not a make and model so don’t expect to be able to ask for a transporter and get it – you’d get something about the same size and shape as a transporter.
AC are a scottish based company so although they don’t have many outlets for hire in your neck of the woods theres plenty in scotland if you encounter a problem
With other hire co’s look out for surcharges for excess milage (AC have an allowance of 250 miles / day but some will have a milage limit per hire and charge per mile beyond that), dumb tricks with fuel etc or just shockingly poorly maintained vans. Often hire co’s will ask you extra over what they’ve quoted for a damage waiver when you collect so make sure you’re getting a price for the full cost of the hire so that you know you are comparing like with like.