The upcoming Vectis auction has this, listed as Gauge 1:
Garden Railway Specialist/Slaters Gauge 1 Wagon Kits Consisting
Saturday 19th March 2016 10:00am
Lot 2442
Garden Railway Specialist/Slaters Gauge 1 Wagon Kits consisting of DG1861 6-wheel Milk Tanker, CM201 GWR Furniture Container, D101 BR 12-ton Meat Van x 2. Unchecked, Near Mint in Excellent boxes. (4)
Estimate: £80 - £120
Presumably the tank wagon is actually Gauge 3, so for that price you'd get a kit and some smaller stuff to sell on and recover even more money.
Curiously, a search of the GRS website shows DG1861 as a transporter wagon, but elsewhere on their site the six-wheeled tanker is indeed DG1861 - just doesn't come up on a search.
Mike