On May 24, 1940 the BEF and the French Army had retreated to Dunkirk under the bombardment of the Luftwaffe and constant pursuit from the Wehrmacht. IOTL Gerd Von Rundstedt ordered the Panzer divisions to halt to repair themselves and recover and consolidate gains to avoid a breakout. Despite objections from Hermann Goring, Chief of Army Walther von Brauchitsch, and Chief of Army Staff Franz Halder, Hitler agrees with Von Rundstedt and orders the divisions to halt. The result was one of the most heroic evacuations as nearly 350,000 war weary soldiers made it safely to Britain. Winston Churchill cautioned the elated public "Wars are not won by evacuations".
The PoD in this timeline is Hitler overrules Von Rundstedt and orders the entire BEF to be annihilated "with deliberate speed". The results are calamitous. The Miracle at Dunkirk is instead the Dunkirk Massacre as over 300,000 troops are either captured or killed. Less than 30,000 escape to Britain.
This deals a crippling blow to the British Army and more importantly British morale. Anti-war protests erupt in London and many government officials advise Churchill to sue for peace. What would happen next? Would Britiain sue for peace as Churchill relents or will he continue the war on the premise of "no surrender"? Say in the comments.