(01 Jan 2016, 5:36 pm)Adrian wrote Boxing Day service iirc. It was before the M1 route was changed to what the 4 is now.
I don't think 4937 has ever been a Washington bus either.
Here is a photograph of the M1 (heading to Easington Lane) on Boxing Day 2008, again in the hands of 4937: https://www.flickr.com/photos/emdjt42/43...7ap-nc97kA
Is it possible it was operated by Deptford, given that it later spent a number of years there, branded as ''Fab56''?