An old slam door DMU▸ was on the Greenford Branch over the weekend. Why? What for?
Not picking up anything special from Real Time Trains -
http://www.realtimetrains.co.uk/search/advanced/CBP/2018/07/21/0000-2359?stp=WVS&show=all&order=wtt - though I do note a series of cancellations late in the afternoon. Perhaps something unusual was scrambled into the slot? The green slam door d(e)mu I'm familiar with and with main line passenger rights is the Hastings set - looking at its diary, I think it was safely tucked up in St. Leonards