When American Express opened its famous blue and white office block in Brighton 25 years ago the company was welcomed as a modern employer who would create hundreds of jobs.

The finance company is now the city's largest private sector employer and over the years most people who live in the area have worked - or know someone who has worked - at the landmark building.

But the company has also become well known for another aspect of its business.

It has encouraged its staff to give back to the community through fundraising, volunteering and donations.

Now it is planning to mark its anniversary with a host of team challenges and fund-raising events across Sussex.

Jo Crockett, the public affairs and communications manager in Sussex, said:

"Good citizenship is one of the company's core values.

"Service is at the heart of our brand so community service is a simple extension of that ethic.

"We have not set a target for the amount the company will raise. We just want to get everyone involved."

The company originally set up shop in Sussex 36 years ago, when it started using a hotel room in Haywards Heath as a temporary office. Amex House was officially opened in September 1977 at a cost of £15 million.

The white nine-storey office block in Edward Street was designed in tiers with blue-tinted windows and has been nicknamed the wedding cake.

It employed 1,500 people, a figure which has now grown to 2,300. At its offices across Sussex, the company now employs a total of 4,000 staff.

It is proud that 26 of those staff have worked for the company for the past 25 years.

The company acknowledges its modern business methods came as a surprise to many of its new staff at the beginning.

As well as working in an ultra-modern building which had the fastest lifts in Europe at the time, staff found it strange to get used to calling their bosses by their first names instead of a more formal approach.

Ms Crockett, who has worked for the firm for nine years and lives in Lancing, said: "It was a culture shock.

The company was much more meritocratic than some people were used to."

She said the company's work practices, including investing in training and staff development, were seen at the time as very modern but are now common methods.

Community work is also now standard practice within many large organisations but at the time it was unusual.

Ms Crockett said: "When you look back it was radically different when we set up shop in Brighton. Now these things are more common."

Ms Crockett believes the company's good citizenship ethos is seen as a bonus to it prospective employees.

She said: "It makes us attractive to work for.

"People get an enormous amount of satisfaction and they learn an enormous amount from taking their corporate skills out into the community.

"For example, having to lead in a different situation is not only beneficial to the community but to the person's own personal development.

"Being with a company that cares for its community is being with a company that cares for its future. Every company needs business success but you need to be operating within a confident and healthy community.

"It is our community - we all use the schools and the hospitals. The quality of life in the community affects us all.

"We are giving people the opportunity to give back to their own community."

Over the years, hundreds of charities and organisations across Sussex have benefited from community work by Amex staff.

Old office computers and equipment is donated to schools and community groups and currently more than 80 employees volunteer to help with literacy and numeracy skills in primary schools.

The company's sports and social club lottery alone raises about £12,000 each year for local good works and East Brighton Education Action Zone has been given thousands of pounds in grants from the Amex Foundation to set up permanent educational projects.

Throughout June, July and August, staff have set themselves a target of 25 community team challenges, which vary from decorating at Coldean Primary School, conservation work on the Downs, building paths for the National Trust and painting work at youth, family and community centres.

The company is also focusing on fund-raising for three local charities:

The Rocking Horse Appeal at the Royal Alexandra Hospital for Sick Children, in Brighton, including organising a sponsored trampoline jump to complete 25 birthday bumps and a 25-mile balloon race from Churchill Square;

Addaction, the charity which helps drug users; and ReMEmber, the Mid Sussex charity for people with chronic fatigue syndrome and ME.

Ms Crockett said no one at Amex had kept track of the amount of money raised by its staff during the past 25 years.

She said it was impossible to put a figure on the benefits to the local community from the money and time devoted by staff.

Ken Bodfish, the leader of Brighton and Hove City Council, said Amex stood out as a beacon for other employers to follow.

He said: "Its contribution to the local economy over the years has been immense and I am confident the roots it has established in the city are here to stay.

"Where the company really shines is in its investment in the city's cultural and social life.

"It is always among the first to come forward with corporate sponsorship for local events and it is a company that generously allows its employees paid time off to help in the community."