The Sheffield company, which employs around 3,000 people and works with governments around the world, needs the capital to cope with "massive" growth.

Mrs Harrison, who featured on the Secret Millionaire TV series, said A4e was at the early stages of negotiations about new work in Spain, Italy and Australia. The company already operates in the UK, Israel, France, Poland, South Africa and Germany.

Mrs Harrison said the company increased its turnover by £20m in the last year and the new investment would give A4e "capacity to grow" even more.

Mrs Harrison, who is chairman, said City investors had shown great interest in the company – and added that A4E has no debt.

She added: "Some of them are looking at investing £30m-40m. We have not had outside investors before. We have got to the level now of such rapid growth that (we decided to) get some outside investors.

"We are controlling the investment very much. We have had a lot of interest but we are absolutely looking for ethical investors."

Mrs Harrison said a minority stake is available in the company, of which she owns 85 per cent of shares. There are 15 other shareholders, who are all employees. She said she would be "very specific" about the investment partner who must be prepared for a "long-term journey".

"It's a challenge to all the private equity people, this one, because they have to have their own money – not some short-term fund. They have to add value to an international business. So many of the PE firms in this country are not international. We are global leaders in welfare reform. They would have to understand what a global marketplace looks like. All of them are very domestic."

Mark Lovell, the executive chairman of A4e, said the company has been talking to some private equity houses but is also interested in broader capital investment, including business angels and individual investors "who are excited about what we do".

Mrs Harrison founded the company in 1987 to provide training and opportunity for people left unemployed by the decline of the steel industry in Sheffield. A4e, which stands for Action for Employment, helps people and organisations get access to training, employment and advice. It now runs mainly public sector contracts from more than 120 service centres across the world.

The mother-of-four is said by the Sunday Times Rich List to be worth £40m although the real figure is likely to be double that.

She was raised in Sheffield and studied engineering at Bradford university. She then transformed her father's small business, retraining redundant steelworkers.

Mrs Harrison, 44, said: "We call ourselves a social purpose company. Social purpose is at the heart of everything we do but it is run on a totally commercial line. We are involved in so many different things and each has a common theme; as long as what we do improves people's lives we are happy to do it."

Leading dealmaker Martin Jenkins, corporate finance partner at Deloitte in Leeds, is advising A4e.