LONDON, Oct 4 (Reuters) - British finance minister Rishi Sunak said on Monday that part of his job was to tell Prime Minister Boris Johnson not to overspend after reports that he told Johnson he would cut up his credit card. "I think that was an old thing, but I think that"s something that all chancellors say, that it"s part of our job," Sunak told BBC radio. "I"d like to think that we have been responsible with the public finances and that"s something that I take very seriously," he said. Sunak was due to deliver a speech to the ruling Conservative Party"s annual conference later on Monday.