The Thames Tideway Tunnel will be a new "super sewer", the width of three London buses, which will run underground from west to east London.
It will be around 20 miles long - and will broadly follow the route of the River Thames, connecting up to 34 sewer overflows.
Sewage, which would otherwise spill into the River Thames, will then be captured in the new tunnel and transferred to a waste water plant in Beckton to be treated.
More top news
The London property market is expected to be the hardest hit as buyers sit it out to see how the economy will be affected.
The former London mayor paid tribute to David Cameron just hours after the Prime Minister announced his resignation.
The pound crashed to its lowest level in 30 years as Britain voted to leave the EU.