Another idea. There is still WW1 that ends on schedule, but perhaps with a few butterflies that result in less harsh Versailles Treaty - or maybe even having the war drag on for another year or two, resulting in an utter annihilation of the Central Powers as they are wracked from the inside by various revolutions. In the end, Germany as well as Russia go red, however, they are taken over by cooler heads, and do not start WWII, instead going towards the Cold War much earlier, by early 1940s. Italy, still under either Mussolini, or his immediate successor, calls itself "The Roman Empire" and embarks on a series of foreign adventures in Africa, but is not quite capable of making much of a dent. By 1950s or so, it is taken over from within by Communists, and becomes a part of the Comintern, which by now controls, directly or indirectly, most of Eastern and Southern Europe (although Turkey and Greece, ironically, are staunch UK/US/France allies, while Spain, though sympathetic to the Comintern, has chosen to remain neutral).
The British Empire began disintegrating by 1960s, with much support for separatist movements coming from USSR/Germany "Comintern" alliance (although the alliance is fragile, and is often in disagreement - think USSR/China relationship of OTL, albeit a bit more cordial). By mid-1980s it is, however, becoming clear that the Comintern economies are beginning to fall apart as they are unable to keep up with more robust Western European and American economies on near-war footing. Although both sides are experimenting with atomic weapons, due to a few quirks down the line a working atom bomb is either never invented, thought of as impossible, or is in very basic stages. Perhaps some sort of a treaty prohibiting the use of atomics - think Hitler's refusal to use chemical weapons for the fear of retaliation, but spread to atomic weapons as well.
By modern day, USSR and Germany are beginning to come apart, however, both still possess major military power, and are under control of aggressive leaders. Knowing that given a few more years, they are on the edge of economic collapse, they launch their invasion of Western Europe, crushing all in their way similar to OTL Blitzkrieg. These tactics tend to work mainly because with no WWII, they are still relatively new, and there are no proper counters designed for them that work.
German and Soviet fleets, while not necessarily as powerful alone as the RN, should be able to survive long enough to make a theoretic crossing, especially with years of preparation, while combined Soviet/German airforce should be a match for RAF in TTL. With control of the Baltic, there is at least a possibility of deploying a large naval force. So, think what would have happened if the Sealion was planned for years in advance by the people with the means, the technology, and the common sense needed to make it work. There you have it - communist Russians and Germans invading the UK some time around 2007...
. As one of my currently maturing plots involves Time Agents getting caught up in the middle of an invasion of britain (modern dayish, not the EU please), I offer the challenge of designing that invasion. The winner gets a starring role...