Chancellor George Osborne and London Mayor Boris Johnson were at a former gasworks which has been deserted for 40 years to launch the scheme. They say the site in Tottenham can now be built on after they removed planning restrictions to get more homes built quickly.
Fifty thousand new homes will be built, 40% of which will be affordable, housing 250,000 people.
More top news
A lamp in the tower which houses Big Ben is to be switched off for the first time in more than 70 years.
Sir Bruce entertained audiences for more than seven decades.
Work in the tower will also pause over the bank holiday weekend.