During an event in Surrey, the Mayor of London, Sadiq Khan, 46, was challenged by a member of the public to come clean over his plans to make the over populated city's air cleaner.
But in his response he has admitted for the first time that the UK's capital will see an influx of as many as another 1.5 million people.
More than five million people have moved to Britain in 10 years with immigration figures showing that more than 66 million people live in the country.
London's population peaked at over 8 million (making it the largest city in Europe) just before WW2, after which it gradually fell to a bit over 7 million by the 1980s. Muslim migrants have since boosted that to back to over 8 million again