It is at the cutting edge of technology - modern, pristine and packed with every possible commercial tool.

However, this hi-tech centre stands silent and empty - the business equivalent of the Mary Celeste.

This is a 'ghost' office where the lights are on and no one is at home until there is an emergency and the building bursts into life as the nerve centre for a business under threat.

If a computer system crashes, plunging a business into turmoil, SunGard Availability Services, the world's leading workplace and IT recovery specialists, takes over.

It provides a vital lifeline to businesses that would otherwise face a logistical nightmare.

Their facilities were used following the World Trade Centre terrorist attacks.

The SunGard service is a kind of insurance that allows companies immediate access to alternative offices where desks, PCs, telephones and a full computer back-up system, geared to their own needs, stand ready and waiting.

This office, on the outskirts of Crawley - its exact location is kept secret for security reasons - can accommodate up to 400 people. It can be up and running as a replica of a client's operation within two to four hours. When relocated employees arrive, they can pick up where they left off in their own office.

Piper Shields, marketing manager for SunGard, said their job was to allow businesses to seamlessly continue their work without their customers ever knowing there was a problem.

She said: "As soon as they walk in, everything is primed and ready to go. Time is money and down time is lost money."

When SunGard takes on a new client, staff carry out a risk analysis and familiarise themselves with the firm's business needs. Then they create an exact replica, right down to the computer programme they use.

Offices also offer creature comforts for the uprooted workforce, including rest and kitchen areas and showers.

Ms Shields said: "Sometimes problems occur at ungodly hours so people arrive and may need to freshen up. We also have pictures and plants around the office to give it a friendly feel."

Not all a firm's staff will be transferred to the ghost office. Many will be instructed to work from home or on laptops, leaving perhaps 20 to 30 per cent of the workforce, plus senior management and crisis teams, to temporarily relocate to Crawley.

Ms Shields said: "While this is happening, we can work behind the scenes to restore whatever went wrong, as long as it is technical. If it is something like a fire then that is down to the client and their insurance company.

"Some functions are time critical, particularly an internet service, and we can often restore that in minutes. Depending on the problem, other functions may take hours or even days.

"Hopefully, their customers can be blissfully ignorant that there is even a problem."

Most companies use the SunGard facilities for just a few days, although some can need them for months. Occasionally, more than one firm will need office space at once.

Ms Shields said: "There is enough room to keep clients separate so they can have confidentiality and privacy."

The Crawley office has thousands of big-name clients, including health care company Bupa.

Ms Shields said: "Our clients come from all walks of industry, from financial and manufacturing to law firms, design agencies, web companies and the travel trade."

The facilities and staff are available round the clock, 365 days a year. Equipment is maintained and tested throughout the year and continually upgraded.

SunGard has a network of 18 similar centres across the UK, offering more than 9,000 recovery positions.