Changes in the interest rate on that day were not expected, the forecasts suggested the unchanged rate of 0.5%. Upon the decision of the Bank of England, the interest rate was not changed. All according to the forecast, all according to market expectations ... But GBP fell. It fell, but quickly retreated, a total spike was about the half of the figure.
Anyway, such a spike stands to reason. There were reasons for this behavior of the market.