Well, the problem for the British was they had to abandon most of their heavy equipment—tanks, APCs, artillery, trucks—that the BEF left on the beaches of Dunkirk. The late summer of 1940 was tough for them. They had men, but were low on everything, including ammo.
Perhaps an invasion by ferry would not be so far-fetched, if the British had no means to offer a defense-in-depth at the water’s edge...
Take a close look at films and photos of British troops hauling ass at Dunkirk and see if you can spot any of them even carrying a rifle. Not very many. They at least could have toted some man- portable stuff back to England.