Operation Sealion was the German plan to invade England across the English Channel in 1940-41; the plan was shelved as the conditions could not be met.
The British Expeditionary Force to France was hurriedly evacuated without its vehicles, artillery and stores from Dunkirk by June 4th, 1940. Other British (and Free Polish) personnel were evacuated from other French ports right up until June 25th, when the French German Armistice came into effect.
The German focus was on finishing the defeat of France, and the chronology of major strategic decisions after June 25th speaks for itself.
July 2nd 1st OKW Directive on the Invasion of Britain
July 13th: Fuhrer Directive 15 – Air offensive to begin August 5th.
July 16th: Fuhrer Directive 16 – 25 Divisions for the invasion.
July 21st: Hitler first tells OKH to prepare to attack the USSR
August 5th: OKW Tables Directive for invasion of the USSR
September 3rd: Sealion scheduled for 21 September.
September 14th: Sealion postponed to 27 September.
September 17th: Sealion postponed, Hitler reviews USSR invasion plans.
September 19th: Invasion flotillas disperse.
It would seem Hitler was never committed to Sealion and that his planned war with the USSR was foremost in his mind.
For their part, Churchill and his military advisers only had to stall for time. They understood the English Channel’s sea states and weather, and knew that an invasion was barely possible in September and impossible after that. Before the Spring of 1941, the British Army would have made good on its equipment losses and England was safe.