I disagree Steel.
As Waton lived through - any pro German feeling had dwindled by the late spring of 1940 and having smashed through the low countries and northern France they were not wanting to let the British escape.
Stretched German supply lines after six weeks of blitzkrieg met determined resistance at the coast from all the British could throw at them.
Remember the Royal Navy had scores of ships which were vital in the success of the operation and had guns that could fire fifteen miles inland and the RAF brought the Spitfire in to the front line in numbers and so could match the Me 109's and let the Hurricanes take on the Stukas, Heinkels and Me 110's.
England was only just over 20 miles away and so civilians were able to muster the flotilla of small ships which enabled the rescue.
I am not painting Dunkirk as anything but a defeat - but it wasn't a defeat in which the Germans could have walked in and taken 400,000 men and materiel prisoner.