Andersen has staked its future on the 'virtual office', in which staff have no private offices or desks. They book space as they would do rooms in an hotel - sometimes a desk, sometimes a meeting area. This means the new building can be used more intensively. Rents are higher than those left in La Defence, but the space is 30% smaller - hence the savings.
That in itself must send a shudder through investors. Andersen is one of those key occupiers expected to demand more space rather than less as it grows over the next decade. And moving back into the centre of Paris undermines the foundations on which the massive La Defence office complex was built.
West European managing partner David Andrews certainly expects explosive growth. 'The European market could triple over the next decade,' he says. But taking conventional offices would be 'too expensive and inflexible.'
Andrew Chadwick, whose group had already begun introducing 'hot desking' to the London office, came up with a radical solution. This is a single organisation called SpaceNet, covering 2,500 staff spread across 16 European offices. New communications technology means there is little difference whether a consultant is in Frankfurt, Brussels, Paris - or even their own home. They all plug into the same 'virtual office'.
Each can connect into the office 'hotel' to contact colleagues and clients, retrieve information or reserve work space. That might be a desk, a meeting room or merely to make an appointment for welcoming a client.
Staff already spend 80% of their time away from the office, so they were ripe for this kind of operation. 'This firmly decouples people from property but also gives Andersen a strong, linked theme,' says Chadwick.
There is also a built-in growth factor. The 7,000m2 Paris building currently serves just over 1,100 staff: its estimated capacity is around 1,600. The aim is to double the size of the European operation without taking more space. The Paris operation will be replicated in each country, aiming at a target ratio of of 5m2 of office space per person.
More work will also take place away from these centres - or 'cities' as Andersen calls them. Andrews says that by the end of the decade, more than 10,000 offices will be in staff homes plus 300 on client sites.
'As more people work from home or on the move, the traditional days of a body occupying a seat in the office are disappearing,' says Chadwick. Buildings can absorb between 30% and 70% of a company's profit, yet a typical office is full for only a fraction of the time. So there is a strong incentive to find more efficient ways of using property, he says.
But intensive activity puts new demands on management. M Jacquenoud, who has switched responsibility from laying out clients' factories to overseeing the shiny new office block, reveals a boyish excitement about the technological whizzery required to prevent the building declining into chaos.
Each staff member carries a plastic 'smart' card which seems to rule their lives. Scattered though the building are card readers and touch-sensitive screens, through which they book work space, track down other consultants or retrieve information. Personal 'greeters' at the entrance welcome visitors, and to emphasise the change in role, Andersen has employed the manager of a top Paris hotel to run the services.
Lounges on the first floor develop this ambiance. Here staff meet each other or consult with clients in a relaxed atmosphere. Other floors are divided into quiet areas, desks for report-writing and spaces for group meetings. Each floor is run by an attendant, who looks after the bookings and ensures that computers, telephones and other services are available when needed.
Papers and files are centralised or electronically 'pooled' so staff can access information no matter where in the world. The firm destroyed 150 tonnes of documents when it left its Tour Gan offices in La Defence and has no intention of going back to old ways.
Personal property, work in progress, portable computers and phones are trundled around in small rolling cabinets, and stored in docking banks until needed again.
No-one has private space - even the executives. In fact, Andrews rails against the term 'partner' as he feels staff should be judged according to how much they bring into the firm rather than job titles.
This sensitivity to staff feelings is crucial to the success of such revolutionary changes in working practices. 'There would have been three ways to ensure that such a move alienated staff,' says M Jacquenoud. 'If partners kept their space when others had to change; if we had moved to a poor building; or if it was seen just as a cost-cutting exercise.
One of the prime objectives in choosing this particular building was to impress staff. It is a spectacular conversion with a semi-circular atrium by architect Jean Michel Willmotts for landlord Credit Foncier. The location is right over a Metro station and a walk away from some of Paris's best shopping. In other words, a world away from the half-dozen anonymous floors of a tower block in Andersen's old home.
The combination of design, location and relaxed meeting areas were also aimed at clients. 'Many more are now happy to come to the office,' says Andrews. 'In fact they have been queuing to see us because of curiosity about what we are doing.'
The firm led the way into La defence 20 years ago as a statement of how it saw the future shape of business, he says. Now it is doing the same for the next couple of decades, moving back into the city and preparing the whole organisation for a new kind of work in the 21st century.
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