Does anyone know the numbers of those stored there ?
WIAs currently stored at Didcot are 7049710018 / 0026 / 0034 / 0091 / 0133 / 0158 / 0224 / 0240 / 0299 / 0307 / 0323 / 0364 / 0372 / 0398 / 0539 / 0562.
Other WIAs may be seen occasionally at Didcot en-route from Cowley to Stoke for maintenance (via Bescot and Arpley), which was the case with the sighting of 007-5 in the original post. Tyre turning is sometimes done at Crewe Electric Depot. The end of the Cowley - Purfleet working no doubt reduced the numbers in traffic, and before that the end of WIA use from Castle Bromwich. For a while after the Purfleet train ended, there was an additional afternoon train from Cowley to Southampton using the Western Docks (with the regular morning train from Cowley using the Eastern Docks) but this second train hasn't run for a while now. The only service using WIAs at the moment is the regular 4O39 09:43 Cowley - Southampton Eastern Docks and 4V39 17:36 return, which runs with a maximum of 10 wagons (which given that each wagon is an articulated set of 5 units, is about 2 wagons short of being half a mile long!)
A surprising photo shows WIAs in the Western Docks in 1996, on a short term flow from Dagenham:
https://www.flickr.com/photos/wilfmeld/49702413216/
The roofs are seen in the raised position. Occasionally the mechanism can get stuck, as mentioned in a comment on a more recent picture from the Western Docks:
https://www.flickr.com/photos/131175774@N06/51303752257/
A couple of contemporary views from the usual terminal in the Eastern Docks:
The first gives a good overview of the QE2 terminal area where offloading takes place:
https://www.flickr.com/photos/169014557@N08/48753632391/
And this one is closer to ground level in the same area:
https://www.flickr.com/photos/chrisperkins/53029755486/
A view from inside the loading sidings at Cowley:
https://www.flickr.com/photos/brianews/5856510104/in/photostream/
Some years ago, I saw a rake of these wagons in a service in Switzerland. I was videoing at the time so it didn’t register until I viewed the footage later.
In the 2000s WIAs were used on two export flows. One was from South Marston, Swindon to Ghent, Belgium for Honda.
This train is seen departing its origin, I think it ran twice a week:
https://www.flickr.com/photos/stevekingd1015/3974143899/
The second train ran from Tyne Dock to Carimate, Italy for Nissan. I seem to remember the Tyne Dock train was weekly, seen here at Peterborough in 2000:
https://www.flickr.com/photos/91977133@N04/16368343924
This would most likely have reached Italy via Switzerland, explaining the sighting of WIAs there.
I think there was also some sort of trial of WIAs in Europe after DB bought EWS - at least one of the wagons that was stored at Micheldever (until they were cut up) had been out of the country for a while before returning through the tunnel for storage.
For reference I'll link an older thread discussing these wagons -
https://www.railforums.co.uk/threads/stored-surplus-wia-wagons.220425/