Joseph Bazalgette created a sewer system which he originally sized for London's needs of the time - he then doubled it to anticipate the future beyond. These are the qualities that I admire.

As an architect, you design for the present, with an awareness of the past, for a future which is essentially unknown.

When the Great Fire of London destroyed most of the medieval city in 1666, Christopher Wren was invited to design a new one. Within days, he had drawn up an elegant grid of broad boulevards leading to majestic squares, but it came to nothing - the existing landowners wanted things as they had been.

Their sewer system is overloaded and there are sewage overflows.

I hope that any expansion of London will learn from the planning examples of some of its most desirable areas such as Chelsea, Notting Hill, Belgravia and Mayfair. All are characterised by high density and a generosity of green spaces.

It would make it awfully difficult to do sewer projects in the future.