The sight of sleek and gleaming machines roaring down one of London's most famous streets on Tuesday will have got many Formula One fans dreaming.
With Silverstone's future uncertain after 2006, what better venue could there be for the British Grand Prix than the nation's capital?
The Monaco Grand Prix is the most glamorous and distinctive race on the F1 circuit - so if they can do it in Monte Carlo, why not in London?
Supporters of a London Grand Prix say that such a race would showcase the capital and boost the city's profile and ultimately its coffers.
They believe the Regent Street demo is a significant step towards achieving their eventual aim.
But could it happen? Will the campaign rev up or will it stall? BBC Sport looks at the obstacles faced by an attempt to stage an F1 Grand Prix on the streets of London.
Money is the bottom line in many sports and Formula One is arguably the most cash-guzzling of the lot.
The rights to host an F1 race are currently in the region of £10-£15m per year.
That is small beer compared to the costs of actually staging an event, which would involve shutting off a not insubstantial section of London's West End.
GP supporters point to the London Marathon, but that closes off a section of the capital for one Sunday morning.
A Grand Prix, with its three days of practice, qualifying and racing, would cause much greater logistical problems, with more of the capital closed off for far longer - and that would mean far greater disruption and expense.
Policing the event, diverting the traffic and setting up and marshalling the course would see the costs spiralling.
With safety now a paramount issue in F1, making a city circuit as hazard-free as possible is much harder than on purpose-built tracks.
Formula One and designer labels go hand in hand but an F1 car hurtling through the window of one of London's most exclusive shops would be taking that relationship too far.
It is a long time since there was a serious accident in Monaco.
But all the drivers agree not only that it is one of the most dangerous tracks on the calendar, but also that the risk of racing there is only accepted because it is Monaco, with all the attendant history and prestige.
Mayor Ken Livingstone says he is "definitely backing" a London Grand Prix, claiming that London's economy would "benefit significantly".
Livingstone, the man who introduced the congestion charge to the capital, says he is giving his support to a Grand Prix on its streets.
But the final decision would not be his alone, and there are many obstacles to be surmounted before it arrives in his in-tray.
Livingstone says a Grand Prix would benefit London
"We would need to negotiate about routes and costs," is the mayor's catch-all proviso to approval.
The London Marathon has become an institution but that is an event which raises millions for charity and which promotes the values of health and fitness.
Contrast that to Formula One, probably the world's most ecologically unsound sport which is also a moneyspinner - but for commercial not charitable concerns.
Even Tim Scott, co-founder of LondonF1.com, a website promoting the benefits of a London Grand Prix, admits: "There would have to be a strong political will for it to happen."
City circuits were once all the rage in F1, particularly in the US, but Monaco and Melbourne (and previously Adelaide) excepted, no race has taken place on city streets since 1991.
That is no coincidence - race organisers are well aware of the financial implications and logistical complications of hosting such races.
Formula One needs an injection of interest, which a city Grand Prix would surely provide - Monaco is the only one of the 10 races this season not to be won by Michael Schumacher.
"Where there's a will, there's a way," says Andrew Scott of LondonF1.com. "The rewards of holding a London Grand Prix far outweigh the inconveniences for all concerned."
But whether London's will proves strong enough once the fuel haze of the world's most sophisticated automobiles has evaporated from Regent Street remains to be seen.