TSB will begin conversion of its 4.1 million Visa debit cards to Mastercard later this year. The process is expected to take a year once the conversion begins. The bank, which was spun off from Lloyds Bank in 2013, has entered into a 7-year contract with Mastercard, which also calls for conversion of its remaining Visa consumer and commercial credit cards to that brand. The TSB credit card portfolio is mostly Mastercard  already. TSB is the sixth largest retail bank in the U.K. and holds between 4% and 5% of all consumer current accounts in the country. TSB is owned by Spain-based Banco Sa...