EURGBP/technical break is an influence
The GBPUSD fell to new day lows while Feds Dudley was being more dovish (at least with regard to September rate change). What may have been a catalyst was a move corresponded with a move higher in the EURGBP suggesting traders may have been scrambling with hedges by selling the GBPUSD
The move took the price toward the swing low on August 12th at 1.5527 (testing now as I type) and below the 1.5553-616 area which the pair has traded mostly above over the last 12 trading days (this is now close risk). TThe 4 PM fixing is also approaching which may be affecting the flows.
Below is a look at the EURGBP. The pair scrapped along a trend line and just recently shot up. This has helped contribute to the GBPUSD weakness. The EURGBP closed at 0.7339 yesterday. The pair is trading above and below the level currently.