Say Oswald Mosley and the British Union of Fascists (or one of the more hard-right National Socialist parties in Britain) got into power well before the war, the people of Britain didn't become increasingly antagonized from Nazi Germany as a result of their fears of German expansionism, and Hitler and this timeline's British Prime Minister managed to foster an alliance. THEN British neutrality in the Second World War is possible, provided the British also abandon their alliance with the French or convince the French either to not support Poland or to loosen the Treaty of Versailles. Without this kind of abandonment of their OTL stances, Britain will almost inevitably end up in a war with Germany. Mutual Anglo-French comradeship at this point was too strong for the Brits to simply abandon France in a war with Germany even if the Germans and the Brits had gotten all chummy recently. Even if OTL Britain and France had kept up appeasement even as Germany invaded Poland, France and Britain wouldn't support Germany, and, if Germany invaded the Soviet Union (or even Yugoslavia, Greece, Denmark, Norway, Holland or Belgium) at this point, Britain and France would probably look at this as the last straw and declare war on Germany then and there.
I read somewhere that Nazi Germany throughout the war attempted to court Indian nationalists into an alliance - maybe if the Germans started early enough and gained enough of a following with the Indian nationalist movement during a war with Britain, they could foster a successful Indian rebellion, and an axis India MIGHT support Germany in a war with the Soviet Union if they were forced to do so. Uh... Sealion magically works and Germany is able to force a British peace settlement with promises of British support in their upcoming invasion of Russia? These scenarios become increasingly improbable the more you look into it. The POD would have to come way back, like if Britain lost the First World War and Britain and Germany somehow both ended up fascist and targeted the Soviet Union together as part of a bizarre alternate World War II. I mean, Italy and Germany ended up on the same side after fighting in WWI, and Italy suffered a fascist coup despite winning the war, so hey, anything's possible.