Some operational pictures of the BEF taken from Peter Taghon's "Mei 1940" which may be of interest to you. Captions are my translations of his comments.
"4.5" Gun Mk 1 towed by a Scammel 6x4 Heavy Artillery Tractor"
Schaarbeek 11/5/40
29/5/40 Westouter.
'...6" 26cwt Howitzer Mark 1 on Mark 1P carriage with Scammel 6x4 Heavy Artillery Tractor.
Rich