Simon Allford raises a cheer for a much-loved oval but is unable to celebrate one of the world's most famous squares
As a Londoner I am drawn to consider two contrasting London "rooms" both created in the early 19th century.

One is a "private" space that attracts visitors from all over the world. Over the past 20 years it has been reinvented by buildings around all but one edge. Its history has inspired architects to create structures that model possible futures yet sit happily side by side, enhancing their historic setting. As with so many of London's great spaces the site has been developed incrementally, yet is well planned, well signed and, one eagerly anticipates, the forerunner to more projects.

The other is a "public" room, similarly famous and much visited. Over the past 20 years its edges have also been remodelled and its landscape remade. Sadly, the 19th century and early 20th century legacy of undersized, overdeferential structures continues. Two international competitions have served only to produce a dreary office building hidden behind an ill-proportioned mock facade and an art gallery that is so in awe of its mediocre setting that it hides behind a large and conceited corner detail.

It is little wonder the first is a place of celebration (bar the odd sporting casualty), while the second is traditionally a place of protest.

The two "rooms" are Lord's cricket ground and Trafalgar Square.