This is a developing story but it appears that the British Pound/US Dollar currency pairing has flash crashed. It dropped from 1.26 to about 1.18 in a matter of 5 minutes. Since then, it has recovered back to 1.24.
The EURGBP currency pairing gained tremendous value after this crash, but has corrected down to the same proportion as GBPUSD.
EUR/GBP
The rest of the forex market has reacted accordingly. Mainstream media should have details soon.