Mary Dejevsky: London's the star. It must stay that way

S how jumping against the backdrop of the Queen's House at Greenwich, cyclists whizzing out of Hampton Court Palace, marathon runners concluding their labours in the Mall after circling St Paul's and Big Ben and – how could the thought not be greeted with a smile? – the near parody of staging the beach volleyball on Horse Guards Parade.

With luck, the fabulous pictures – not just of the capital, but of the countryside and coast – that have been beamed around the world over the past couple of weeks will serve not only to introduce foreigners to our country, but to reintroduce it to ourselves. And once the Olympic season is over, I for one hope there will be a rush not just to the sports clubs, but to societies and lobby groups concerned about the quality of architecture and city planning.

The Olympics have shown how London can look, when its stone façades have been cleaned, when traffic lights have been culled, when parking and loading regulations are enforced and when the accumulated clutter of street signs is replaced by notices that are stylish and informative. They have shown that we do not need to have juggernauts pounding inner-city streets, that even our public transport can work and that, in fact, a lot of traffic is not essential to keep a city running.

London can look, feel and function like a more relaxed and liveable Continental city – if it really sets its mind to it.

But the pictures also show that we have a city, in its buildings, streetscapes and skylines, that is worth looking after with much more care than we currently do. That does not mean conservation at all costs. The Shard has been controversial, but at least it's distinctive. One of the most egregious failings of London planning is that many new buildings, including those in distinguished surroundings, have no character, and even less sense of place; they could be anywhere, and they are invariably too big.

I have attended Westminster Council planning meetings where developers produce reams of highly technical documents about tiny fractions of light and height, in defence of structures that actually exceed the regulations in both respects.

They receive permission on the grounds that the limits have been breached only a little (even though this results in continual new norms), that the expensive plot might otherwise lie fallow and that they accept the developers' descriptions of their pedestrian hulks as being "of merit".

The results can be seen all around us, in the bits of London the Olympic television cameras have skipped; in the piecemeal disgrace that is much recent riverside development and in the failure to respect the good – whether architecture or space – that is already there. Much is already being spoken about legacy: a new emphasis on sport and the regeneration of London's East End. But a third legacy, no less urgent, should be a revolution in city planning.