A rift could be growing within the coalition government over the future of the UK's banks after business secretary Vince Cable again called for a split of their retail and investment businesses.Commenting after the appointment of Barclays' investment bank head Bob Diamond as the bank's new chief executive, Cable said the government must follow through on plans to split the "casinos" away from traditional bank activity.The coalition government has set up a banking commission to look into the future structure of the industry. Several banks have indicated they could leave Britain if it recommends a separation of businesses, most notably HSBC, but Cable said in a radio interview this morning he wants "strong" recommendations. While not directly criticising Diamond's appointment he said that it raised "the wider policy question about how banks can be made safe, and we are worried about this combination of the casinos and the traditional banks.""I think it does illustrate the wisdom of the Government's decision to set up this banking commission to look at the structure of banks," he added."Mr Diamond illustrates in a particularly graphic way where you have an extremely high-paid head of an investment bank taking over one of these retail banks," Cable said.