Mumbai, Sept. 19 -- The British pound is seen tumbling against the dollar on Friday to around one week low from a two and half month high attained earlier in the week. GBP/USD is quoting at $1.3506, down 0.37% on the day. The pair fell despite positive data from UK showed retail sales climbed 0.5% month-over-month (MoM) in August after advancing 0.5% in July. Core Retail Sales, stripping the auto motor fuel sales, rose 0.8% month on month in August, compared with the previous rise of 0.4% and annual retail sales increased 0.7% in August versus July's 0.8% revision. The pound is already facing challenges after the Bank of England decided to keep interest rates steady at 4% yesterday. Moreover, firmness in dollar overseas after Fed sounded ...