Seen through what once was the brass-plated letter box of 65 Regent Street, and is now a hole in the wall, is a pile of rubble. Standing outside are two rather handsome Frenchmen. They perspire slightly into their pale linen suits. But most men in their position would be sweating buckets: they have plans that will either transform the heart of London, or ruin them.

They are Pierre Condou and Bruno Loubet. The former is a 38- year-old refugee from the diamond trade (he says he still 'dabbles'). The latter is the 32-year-old chef from Bordeaux who started as a lowly commis chef in London 12 years ago, and who last year gave up his Michelin star at the Four Seasons Hotel on Park Lane to work with Mr Condou.

Together, by the autumn, they intend to have transformed the former British Airways offices behind them to a 200-seat restaurant, tentatively called the Odeon.

There are only a few snags. Westminster Council has denied planning permission for any new restaurant frontages on Regent Street. And the Frenchmen may have to rethink the name Odeon, due to something called a 'passing-off action' initiated by a chain of cinemas.

Condou and Loubet seem to have entered what amounts to a space race among London's Anglo-European restaurateurs (an ancient sport among the Chinese and Malaysians, who have always believed in great barns of restaurants). The Odeon, with its 200 seats, will be a middle-sized giant. By comparison, Kensington Place has 132, and the Atlantic has 150. It is Sir Terence Conran who pushes the body count into dizzying numbers: Quaglino's alone has 350 seats, the restaurants comprising his Butler's Wharf Gastrodrome a total of 771.

What the Odeon lacks in size, Condou and Loubet hope it will make up for in location. Well, Regent Street certainly sounds classy. It brings to mind Aquascutum, Hamley's, Mappin & Webb. Number 65 overlooks the choicest patch, where John Nash's original 1812 design gave the street a graceful bend to avoid cutting a swath through St James's.

'Floodlights will light up the arch,' says Mr Condou as he gestures to the passage leading into Air Street. (It seems that complying with the council's frontage restrictions simply involves putting the entrance round the corner.) As I stare obediently, a blue Transit van nearly reverses over us before parking illegally.

'We'll have to stop that,' Mr Condou says. They will have to stop a lot of things, first and foremost the steady, 94-year decline of Regent Street into a smoggy strip of chain stores and camera-wielding tourists wearing Hawaiian shirts.

As we stand outside Number 65 I wonder if, despite their long tenures in London (30 years for Condou, 12 for Loubet), they have realised that most Londoners do not frequent Regent Street - in fact, they actively avoid it. What do Londoners want with chintzy china shops, currency exchanges, houses of tartan? They even hate the Christmas lights.

Great swirls of dust rise as we enter the building. Mr Condou, with a sweeping gesture, says: 'This will be a spiral staircase - no, not spiral, just a curving staircase.' (This was a relief: I thought it was the dining room, and it looked a bit small for 200 people). Upstairs was more like it. Even gutted, it is a lovely room, 67 metres long, which spans out in a gentle curve echoing the bend of Regent Street itself. The curve is picked up and complemented by a series of arched windows. These are grimy, and thick dust hangs in the air, but the room is still strangely magical, its length and repeating windows inducing a similar sensation to that of standing in a hall of mirrors.

The view over Regent Street is mesmerising: Routemaster buses chug by, motorcycle messengers nip through traffic. It is like a back projection for a Cary Grant film, but it is real. One thing is certain about this unborn restaurant: the turnover on the window tables will be slow.

It is Mr Condou's wife who is the property dealer. She would know we had blundered by saving the best for first. The rest of the tour was dark, dirty and dutiful: nods and murmurs as I am told the bar will be here, the display kitchen there. A cave behind that will be the kitchen. Then, up and down winding stairs, there are dark expanses where will be food stores, wine stores, staff-rooms, larders, loos.

Occasionally I steal glances at the two gentlemen, and from their eager expressions it is clear that we are not sharing the same experience. I see 15,000 square feet of rubble, they see glamour; I smell exhaust, they smell oxtail simmering; I hear the builders hammering and traffic roaring, they hear laughter, a piano tinkling and corks popping.

It is no wonder their imaginations are in tune. They have known each other since Mr Condou opened the fish restaurant, L'Hippocampe, in Fulham, west London, in the Eighties. Yet they did not become partners until L'Hippocampe moved to Frith Street in Soho in 1990, and was immediately buffeted by the recession. Lowering prices was out of the question: fresh fish is too expensive.

By 1993 they were partners and, appropriately enough in an era of chef-worship, L'Hippocampe had been renamed Bistrot Bruno. There they served weird-sounding but good-tasting stuff: scallops and piccalilli, or fried trout with sour cabbage and smoked herring cream. There are still some flourishes, but the menu has calmed down. Now one might find salt cod puree with french beans and tomato dressing, or pork sausages with roast apples and shallots.

Both gentlemen are somewhat cagey about menu plans. In fact, Mr Condou could enjoy a second career as a government spokesman. When will the Odeon open? 'Autumn is as close as I will say at this particular juncture,' he says. What will its food and wine cost? 'Essentially value for money is going to be our leitmotif.' How much will it cost to set up? 'I'm not prepared to say.'

I left the interview hoping they are not in over their heads, and that I will be able to afford a south- facing window table occasionally.

(Photograph omitted)