Alan, I can confirm that what you were originally looking for is indeed PINE BARK WOOD-CHIPS used where I live in Southern California and in various other parts of the USA for garden landscaping purposes and commonly available at garden supply stores and big hardware chains like Home Depot and Lowes.
The big difference between pine bark wood-chips and CORK BARK is the size -- cork comes in much larger pieces, so large I would refer to them as "sheets" or for the smaller tunnel-like pieces "rounds".
The up side of this is building terrain with them requires much less work, since you don't have to glue a gazillion individual chips together in order to form a decent-size terrain piece. The down side is simply the price, as cork bark is far, far more expensive than pine bark wood-chips.
Of course, the devil is in the details, and it seems that finding pine bark wood-chips in the UK is now something of a challenge. The obvious problem with ordering such material internationally would be shipping costs, which might make it as expensive as custom-ordering a finished rocky hill or mountain from a professional terrain-builder.
If any British wargamers looking for pine bark chips are considering a trip to the USA, I suggest you leave some room in a suitcase and stop by a garden shop, where for less than $10.00 USD you can get a 57 liter bag, able to cover 2 cubic feet -- 48" x 48" x 1" deep -- enough to construct a ton and a half of terrain.
Pine chips:
Cork "round":
Cork "sheet":