There's a clue in an extract from a 50th. anniversary book for RAF Stafford. I quote -
" The first receipts and issues recorded in the Unit's own right were in May 1940, and comprised 1,231 tons 9cwt. received and 54tons 18cwt. despatched. Similarly, the MT Squadron's activities and workload escalated rapidly, so that by June 1940 the vehicles were running almost 30,000 miles a month. While the role of 16 MU, in the Battle of Britain, was directly quite limited, attitudes changed markedly and developed a much more urgent approach to meeting the RAF's needs"
In the same book - July 1941. 5,704 tons received, 4,123 tons despatched and 223,548 miles driven by MT.