How many bricks are there in London?

Assumptions:
'London' = innter and greater London

Estimates:
8million people in London
Average 2.5 people per household
Average size of dwelling around 1000 sq ft
90% dwellings made from brick
Average dwelling = 8,000 bricks including internal walls and driveways etc.
Public buildings are made from brick
Public buildings ofset those dwellings not made from brick
Brick yards contain a small % of total bricks
Buried old bricks are discounted


Calculations:
8,000,000/ 2.5 = 320,000 dwellings
8000 x 320,000
= 25,600,000,000 bricks in London