The bank offered $40 million and said it had sold $38.2 million at a cut-off price of 7.1401 pounds to the dollar, unchanged from its last sale on Monday.
The rates at which banks are allowed to trade dollars are determined by the results of central bank sales, giving the bank effective control over official exchange rates.
In the unofficial market, one trader said the pound was trading at 7.81 to the dollar on Wednesday, while another put the rate at 7.80. Traders said the pound was trading at 7.81 to the dollar on Monday and 7.80 on Sunday.