That's bollocks. Churchill was certainly a racist. A man of his times, when racism was not only normal, but many people believed it was scientifically validated. He also spent the 1930s complaining about more rights (or even home rule) for India, which is obviously a lot less worthy than his constant (and correct) warnings about the Nazis.
He was an imperialist too. Though you'll find that the current national curriculum covers the British Empire, and why taking over a quarter of the world was a bad thing. I see nothing in modern British culture to suggest that we haven't accepted that the empire was "a bad thing<sup[TM]</sup>". And Britain has consistently been one of the world's largest foreign aid donors, providers of peacekeeping troops, supporters of global institutions and norms, since the war. Partly as a result of an imperial past.
But you'll have to come up with some justification for "genocidal" (which has a specific meaning). Or admit you're talking bollocks.
Come to think of it, mass murder as well. The bombing of German and Japanese cities is an interesting moral problem. After Dresden, it's clear that the British were beginning to have their doubts. Churchill pissed off Harris by criticising him for that, and changing policy. The Germans were also particularly criticised for terror bombing in Spain, and at the start of the war. So it was obviously seen as immoral. On the other hand, it was the only offensive tool the British had against Germany after the fall of France. And it was the committment to the bombing that did a lot to convince neutral opinion that Britain was serious, and intended to continue to fight until Germany was defeated. Would the USA have joined the war in Europe after Pearl Harbour if the phoney war had resumed after the fall of France - or just fought Japan? Also without the air attacks on Germany, would they have been able to beat the Russians in 1941 or 42? Admittedly the Germans made a pisspoor job or running their war economy, production actually peaked in mid 1944, according to the US Strategic Bombing Survey after the war. Because they didn't really start operating a planned economy until 1942 - and even then they wasted too many resources on having too many different models of tanks and planes, rather than just picking one, and bashing out lots of them.
Anyway it's a lot more morally complicated. Mass bombings of civillians are now unequivocally illegal. But then nowadays we have the technology to do precision bombing. Again, according to the US Strategic Bombing Survey, only 2% of bombs dropped in WWII fell within 500 yards of their target.