While I as back in the UK the other week I grabbed a handfull of B & W Prints to scan when  I got back to Ng.    This lot are dated 20th March 1967 and where taken between Chiltern Green & Harpenden  Junction.    They note that the Tartan Arrow was a test train.  Looks (if my memory is correct)  like it is on the Up slow lines.    I hope these are of interest to some one.      Trev.