This could only happen in Britain. Central London's parks heave with people in the summer; the scraps of green between the picnics shrink as millions of people - every lunchtime, every warm evening, every weekend - squeeze themselves into parks designed for a fraction of this kind of use. As one of the biggest tourist attractions in the world, the city sucks in millions, and many millions more come to work: all of them need space to rest and relax. The park keepers struggle against all the odds to provide beautiful green spaces for them to do that. While new buildings are going up in every spare corner of the city, there are precious few initiatives to build new parks to accommodate this rising population density.

It is most acute in the beautiful, small parks of St James and Green Park at the heart of city, but look on a map and the absurdity is immediately apparent. While Green Park is used by up to a million people a month in the summer, right next door a park of near-comparable size remains largely empty; pristine lawns behind 10ft brick walls, bristling with barbed wire and metal spikes.

Buckingham Palace Gardens is the largest private green space in central London. The forbidding walls ensure that Her Majesty's subjects do not even have the pleasure of seeing the trees, bushes and shrubs, let alone visiting them. No, the gardens remain for the private pleasure of the Queen, and she is not even there much of the time. She's away in August - a peak month for park use - and September; many weekends she is at Windsor or Sandringham. Of all people, the Queen does not need a park to herself. Of course, there are the garden parties - three a year and 8,000 guests at each - and Buckingham Palace press office is keen to point out that there are occasional additional parties. Let's be generous and conclude that perhaps as many as 30,000, on average, visit the gardens a year - for an hour or two.

The Palace is also eager to add that grateful subjects of Her Majesty are now allowed as part of their tour of the state rooms in August and September, to walk along a 500-yard path through the gardens. But they have to stay behind cordons under the watchful eye of attendants - and it costs £15.50 per adult.

Nearly 10 years ago Terry Farrell rightly questioned this absurd use of space and proposed opening up the gardens and linking them to St James's Park and Hyde Park to make an extraordinary belt of green space across the capital. It's a great idea, but where was the clamour to back him up, and to insist that this land belongs to Londoners and London's visitors? Why didn't we shout more loudly so that we could be heard even over those monstrous walls? What makes us so supine?

So here we have it: the Queen could follow in the tradition of many of her forebears who opened Royal parks to the public - King Charles II was first with St James's; Green Park was opened in 1826 and Regent's Park in 1835. She could announce it now, so that the work of dismantling the Berlin Wall-style defences could be completed for a grand opening in 2012, a fitting tribute to an Olympic city, and the best imaginable legacy for such a long-reigning monarch.

For the millions who pour through Victoria station, there would be some relief close to hand; the gardens would be a welcome for new arrivals. A place to sit and wait, a place to meet - a green hub next to one of the busiest transport hubs in the city. The Queen could see the sense and do it off her own bat, or we could say, finally, enough's enough, we want the gardens back by June 2012. Either it's her decision or it's ours. Ken Livingstone wrote yesterday on these pages that he's planning on some gardening: perhaps he can start his comeback with a campaign to get our gardens. Anyone else up for it?

m.bunting@theguardian.com