According to this article:
Churchill didn't like Gandhi.
Is it true? Why he didn't like him?
This may possibly have something to do with Ghandi at best seeing little difference between Hitler/Nazis and Britain and totally opposed anti-Nazi war; and at worst, being friendly with Hitler for the longest of time (src for the latter).
Hitlerism will never be defeated by counter-Hitlerism. It can only breed superior Hitlerism raised to nth degree. What is going on before our eyes is the demonstration of the futility of violence as also of Hitlerism.
I appeal for cessation of hostilities, not because you are too exhausted to fight, but because war is bad in essence. You want to kill Nazism. You will never kill it by its indifferent adoption. Your soldiers are doing the same work of destruction as the Germans. The only difference is that perhaps yours are not as thorough as the Germans. If that be so, yours will soon acquire the same thoroughness as theirs, if not much greater.
I do not want Britain to be defeated, nor do I want her to be victorious in a trial of brute strength, whether expressed through the muscle or the brain. Your muscular bravery is an established fact. Need you demonstrate that your brain is also as unrivaled in destructive power as your muscle? I hope you do not wish to enter into such an undignified competition with the Nazis. I venture to present you with a nobler and a braver way, worthy of the bravest soldier. I want you to fight Nazism without arms, or, if I am to retain the military terminology, with non-violent arms.
I would like you to lay down the arms you have as being useless for saving you or humanity. You will invite Herr Hitler and Signor Mussolini to take what they want of the countries you call your possessions. Let them take possession of your beautiful island, with your many beautiful buildings. You will give all these, but neither your souls, nor your minds. If these gentlemen choose to occupy your homes, you will vacate them. If they do not give you free passage out, you will allow yourself, man, woman and child, to be slaughtered, but you will refuse to owe allegiance to them.
Hitler killed five million Jews. It is the greatest crime of our time. But the Jews should have offered themselves to the butcher's knife. They should have thrown themselves into the sea from cliffs. As it is, they succumbed anyway in their millions.
"Can the Jews resist this organized and shameless persecution? Is there a way to preserve their self-respect, and not to feel helpless, neglected and forlorn? I submit there is. ... If I were a Jew and were born in Germany ... I would claim Germany as my home even as the tallest gentile German may, and challenge him to shoot me or cast me in the dungeon. ... And suffering voluntarily undergone will bring them an inner strength and joy. ... The calculated violence of Hitler may even result in a general massacre of the Jews by way of his first answer to the declaration of such hostilities. But if the Jewish mind could be prepared for voluntary suffering, even the massacre I have imagined could be turned into a day of thanksgiving and joy that Jehovah had wrought deliverance of the race even at the hands of the tyrant.
I do not want to see the allies defeated. But I do not consider Hitler to be as bad as he is depicted. He is showing an ability that is amazing and seems to be gaining his victories without much bloodshed. Englishmen are showing the strength that Empire builders must have. I expect them to rise much higher than they seem to be doing.
Gandhi was an Indian Nationalist, who wanted India to go its own way, which means independent from the British empire.
Churchill was a British politician, who wanted to maintain the dominance of the British empire over the British colonies.
Basically, their political goals were incompatible. With respect to the question of Indian independence, they were political opponents.
Apart from the reasons pointed out by other answerers, there was another reason for Churchill to hate Gandhi.
Gandhi invented a new technique to protest called Nonviolence.
If we look at this video, we can see how Hindu revolutionaries adopted this technique to protest. At the core of this technique, it was protesting through civil disobedience. This was an ingenious technique which gave Gandhi an upper hand in front of mighty British administration.
If we look at the history of British Raj, we can see that armed rebellions and revolts were routinely crushed by the British government as they had superior firepower. But, the British government didn't have any tool in their hand to counter this new form of protest. This gave Churchill a chilling feeling that he is slowly but consistently losing the grip on India.