London mayor Sadiq Khan today joined forces with Bank of England Governor Mark Carney to try to reassure the money markets.
The pound crashed to its lowest level in 30 years as Britain voted to leave the EU.
More than £100bn was wiped off the value of FTSE 100 companies within minutes of the start of trading in the City.
Mr Carney made a speech shortly after David Cameron announced his resignation saying some volatility was expected.
Mr Khan sent a message to global businesses and investors saying: 'There is no need to panic.'
The mayor, who backed the Remain campaign, praised David Cameron for his 'dignified' resignation speech.