Mary Dejevsky: London has looked fabulous. Can we keep it that way, please?

The pictures show that we have a city that is worth looking after

Show 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.

It was these images – starring segments from the promotional video shown in Singapore – quite as much as the big idea of the UK capital bidding to host the world's greatest sporting festival that hooked me on the idea of London 2012 from the start. Just imagine what fun Lord Coe and the rest must have had, standing in front of a huge map of London, indulging in ever higher flights of fantasy as they plotted where individual events belonged.

Seven years on, the reality soon surpassed expectations. Even through the pouring rain, the early stages of the women's marathon on Sunday looked gorgeous. The rain actually added character, as colourful umbrellas contributed to scenes that were almost Renoiresque. By then, many hardened sceptics were starting to admit that they might have got it wrong about London 2012, though with less humility than we proto-enthusiasts might have hoped.

The pictures have been spectacular. Equestrian events in Greenwich have brought us sequences of immaculately groomed steeds framed by the Old Royal Naval College and the skyscrapers of Canary Wharf. The marathon route takes in City landmarks such as Leadenhall Market and the Monument, as well as St Paul's. The design of the stadium at Horse Guards Parade leaves the Whitehall side low, to show off the buildings behind.

By and large, foreigners – the French included – suspected we could do it. Overseas diplomats in London are some of the greatest devotees of their surroundings. I know of one who spends weekends travelling on the upper deck of buses, relishing the views. Another, who spent his free time cycling in the West Country, could have been a one-man advertisement for the Devon tourist board. And more Dutch citizens than you might expect keep second homes in the Kent or Sussex countryside; they are here as Britophiles, not tax exiles.

A German friend once chided me, saying that we natives were too cavalier about our capital. Central Westminster – Parliament Square, Westminster Abbey, the Houses of Parliament – she said, was one of the most glorious architectural ensembles in all the world. She was right. But it is just one of so much we belittle or take for granted.

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 glorious 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.

As an interested member of the public or neighbour, 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.