(Reuters) - London's FTSE 100 swiftly climbed to a session high as its international stocks got a lift from a hit to sterling after the Bank of England cut its economic growth forecast, adding on to earlier cheer that was brought on by the Fed's softer stance. The FTSE 100 index was up 0.7% with BP and Shell both up more than 1% after Middle East tensions drove crude prices higher, while the FTSE midcap index was up 1% at its highest in a month by 1154 GMT.The pound trimmed gains after the BoE..