Médecins du Monde, a Paris-based organisation that has provided humanitarian, non-governmental help around the globe for more than 20 years, is taking the controversial step with the help of volunteer doctors and nurses, most of whom work for the NHS.

Like the health professionals who staff the charity’s clinics in Africa and Asia, they will give their time free to help the needy and vulnerable.

The charity’s decision to open three medical centres will come as a huge embarrassment to Patricia Hewitt, the new Health Secretary, and suggests that one of the key founding principles of the NHS — that it is a universal service — no longer holds true.

A spokesman for the charity, which has a London office, said that the initiative, to be called Project: London, would be expanded to other major British cities if it were a success. She added that an initial group of volunteer doctors and nurses had been trained in how to operate the clinics, which should be open by July or August.

The Healthcare Commission has given preliminary approval to the three clinics, in the premises of local charities, and is due to make a final inspection within two months.

The clinics will aim initially to provide free basic primary healthcare to homeless people, refugees, asylum-seekers and street sex workers.

The move is likely to be well received by British charities representing Médecins du Monde’s target clientele.

Tarig Hilal, of the homelessness charity Crisis, said that the lives of homeless people, on the streets or in overcrowded hostels or bed-and-breakfast accommodation, made it inevitable that many would experience extremely poor health.

Yet a lack of a permanent address, fear of discrimination, poor attitudes among health professionals, full GP lists and mental health problems meant that they often did not get the healthcare they needed and were entitled to. When they were able to access care, many with chaotic lifestyles found it hard to cope with the rigidity of appointment systems and waiting times.

A spokeswoman for the Refugee Council said: “We know of people who have been turned away from GP surgeries because receptionists have thought they were not eligible for treatment. In other cases, GP lists are full and they are simply unable to register.”

A government decision last year to deny NHS care to failed asylum-seekers had caused further confusion about eligibility. “Many don’t know how the NHS works and don’t understand how to register with a doctor or where to go,” she said. As antenatal screening and childbirth were considered secondary care, many refugees and asylum-seekers were not eligible to receive it, she added.

Karen McColl, director of Médecins du Monde UK, said the charity had been conducting a needs assessment in the past two years looking at access to healthcare in East London.

“Providing healthcare to marginalised people in developed countries, as well as developing ones, is an integral part of the humanitarian work of the 25-year-old MdM network,” she said. “The overall aim of Project: London is to improve access to mainstream health services.”

Health officials were more circumspect about the project, saying that they were already catering for Médecins du Monde’s target population. Carolyn Regan, chief executive of the North East London Strategic Health Authority, which covers the East End, said: “One of the central things we already do, we feel very successfully, is to invest a lot of effort and time into providing health services for precisely these groups.

“We work with a number of other organisations and if Médecins du Monde does set up clinics, we would be very happy to talk to them.”

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