The Battle of Britain Five Months That Changed History, May—October 1940 by James Holland (z-lib.org).epub

By mid-morning the trucks were loaded and the men were on their way.
‘God helped our retreat by sending a thunderstorm to darken the skies,’
noted Stan, ‘and although it made our journey rather uncomfortable, we
were really thankful for this protection against the bombers.’ Stan was
shocked by what he saw as they trundled north: even more abandoned
vehicles, stores littered across the road, corpses lying in fields and ditches,
houses and buildings bombed and blazing. The journey became slower and
slower as they joined more traffic, troops and refugees. Eventually, near the
perimeter, they were forced to ditch their trucks. With rifles, one Bren and
one Boys anti-tank rifle, plus as much food and ammunition as they could
carry, they began marching.
Eventually, they reached a farmhouse where the colonel had told them
to rendezvous – Stan and six others had remained behind to destroy the
vehicles and other equipment. They were still not sure what they were
doing but the Assistant Adjutant, now the senior officer, gave them a talk.