Despite Derby Lightweight single car 975010 Iris spending over thirty years in departmental use, I only saw it once on the mainline. For well over half of that time it was painted in Derby Research red and blue livery with large 'Test Coach Iris' lettering on the side. By the time I eventually saw it, it had just been repainted into original green livery, albeit with a half yellow panel in place of the original speed whiskers. The unit was one of two single car Derby Lightweights introduced in 1956 (as 79900) for the Banbury to Buckingham service. It is pictured here heading south at Claydon on 14 March 1994. The by then unique unit survived in departmental use until 1999, although at the very end of its life it had to be sandwiched between two Class 101 vehicles, due to problems with its non-standard AEC engines. Luckily this interesting unit has been preserved.