Treasury chief Gordon Brown - likely to succeed Tony Blair as prime minister by September - said Sunday that any future government had lessons to learn from the aftermath of the Iraq invasion and that he would not shy away from criticizing President George W. Bush. Brown acknowledged mistakes had been made in planning over Iraq and said he believed the ideological battle for the hearts and minds of young Muslims was as crucial as the battle against communism in previous generations. Blair has said he will step down as leader of the governing Labour party and prime minister before September, with Brown unlikely to face any credible challenge to replace his colleague. "I look forward, if I am in a new position, to working with the President of the United States, George Bush. Obviously, people who know me know that I will speak my mind. I will be very frank," Brown said in an interview with British Broadcasting Corp. television. "The British national interest is what I and my colleagues are about."