Normally they would work by determining supply against demand.

Right now the only people that want the pound are people who have unavoidable business with the UK. Investors in GBP likely do not want to trade their currency for another nations currently because they are hopeful that the GBP will return some of it's value so it's better just to move it around the UK for now.

However, the UK does still need to import a vast amount of things almost 30% of our gdp is spent on imports. This is causing a huge gbp supply to demand deficit that the BoE and other central banks are bailing out. They are artificially limiting supply of gbp each day and/or using their own reserves of foreign currency to buy the pound. This is being done every day to to prevent any large drops in value and to make the pound appear stable.

The currency traders that they're talking about only buy and sell around the peaks and troughs of the market. While there are still traders at the moment. They are trading on government interventions that cause a turn in direction in the pounds value. Every day they continue to buy, every day they continue to sell. But nobody is willing in the current climate to sit on a large stockpile to sell at later date because when the pound will return to it's former exchange rates is big unknown right now. Better to make 100 small profits than risk it all on 1 big trade. Ultimately though this trading has no effect on the value of the pound compared to bailouts and intervention the BoE is using to prevent free fall.

This allows the BoE to essentially choose which Tory candidate they want. If they don't get what they want "oh no a financial crisis".