A friend recently needed to move EUR sitting in one of her HSBC accounts to GBP in another of her HSBC accounts. To get HSBC to do it would have taken "up to three days", and the exchange rate was abysmal. On my recommendation, she used TransferWise instead, saved almost £300 on the exchange rate and it moved within an hour. YMMV, but in UK I've literally never seen big banks be cheaper than TW.