Was in my local Wilkinsons in Ilford today and they were clearing these out. No big signs, just a small price label added to the box saying it was £5. Probably why they had some left.
Its the walk in medium size greenhouse. 120cm wide, 190cm high, 190cm deep. Includes staging for one side.
There were still around 5 on the shelf when I left. Not sure if national but would be worth a look.
Bigger image here as it's not listed on their site any more so can't provide a product link:http://www.wilko.com/content/ebiz/wilkinsonplus/invt/0260896/0260896_m.jpg
This is a bargain price.