That's roughly what they are. They are known as 'Kirov tilting wagons' and they carry out of gauge panels for switch and crossing (
S&C▸ or points) replacement. The yellow framework sections you saw in the Banbury shot are in the travelling mode (at about 60 degrees away from horizontal), and are lowered once on a worksite.
News item here refers:
http://www.rail-news.com/2009/11/26/tilting-wagon-delivers-milestone/The key point is that S&C panels can be manufactured and tested under factory conditions and moved to their intended location without having to be dismantled and then reassembled trackside, hence speeding up renewals.
Found a set of four videos with a complete train including the Kirov rail crane unloading the panels:
http://www.youtube.com/watch?v=aATnpHQUNUwPaul