It is, of course, difficult to know what sort of hidden agenda might have been in Churchill's mind when he gave this speech. It is clear that Churchill was strongly anti-communist and that he was very suspicious of Stalin and the USSR. His desire to warn the world of the threat they posed was surely his main goal for this speech.
However, we could argue that Churchill was being self-serving when he gave the speech. He had not long before been voted out of office as Prime Minister. His party had lost to the Labour Party, which was a much more leftist party. In giving this warning, he might have been trying to imply that Labour was part of the threat from communism. He might also have been trying to make sure that he remained in the public eye as a major leader so that people would be more likely to vote him back into power.