The effect of speculato's on an exchange rate

The effect of Boris speaking in favour of Brexit: Thanks to the FT
http://www.tutor2u.net/economics/blog/sterling-drops-on-brexit-uncertainty?utm_medium=email&utm_campaign=Economics%20daily%20digest%20Wed%2024th%20February%202016&utm_content=Economics%20daily%20digest%20Wed%2024th%20February%202016+CID_cd6e78ca24ac76045893f9c212ff42f1&utm_source=CampMonitor&utm_term=Sterling%20drops%20on%20Brexit%20uncertainty%20Katie%20Martin%20from%20the%20Financial%20Times%20here%20looks%20at%20the%20Boris%20effect%20-%20which%20saw%20a%202%20drop%20in%20the%20value%20of%20the%20pound%20the%20largest%20drop%20since%202009%20and%20markets%20are