As Richard Wheatcroft, director of MBA programmes at the Open University - the biggest distance learning MBA provider in the UK, if not the world - points out, the number of people who can afford to take one or two years out of their working career to do a full-time MBA is relatively small.
"They are either whizz kids in their twenties who have not got family responsibilities or mortgages," he says, "or they come to do the executive MBA, where the company chooses to send a senior manager off for nine months or whatever."
Distance learning programmes are, however, often the only option for middle managers trying to deepen their understanding of the theoretical framework of the way they conduct business.
"Distance learning, and to a lesser extent part-time programmes, has opened up the MBA to a clientele that were frankly not able to access it at all before," says Wheatcroft.
The MBA programme at the OU is now the largest programme of its kind accredited by the Association of MBAs in the UK. The OU's programme represents 20 per cent of all MBAs studied in the UK and 40 per cent of all distance learning MBA enrolments.
In 1997, more than 27 per cent of MBA graduates surveyed by the association came through the distance learning route. Today there are some 25,000 people enrolled on the OU's certificate, diploma and MBA courses - of which 18,000 are in the UK, 6,500 in Eastern Europe and 500 elsewhere. Of these some 8,600 are enrolled on the MBA course.
The number of students enrolling for the MBA, which offers open access via its diploma foundation programme, has grown steadily since its inception in 1989.
Henley Management College's distance learning MBA is the next largest programme with some 6,500 MBA distance learning students in the UK, South Africa, Hong Kong, Malta, Cyprus and elsewhere in the world. Other schools whose distance learning programmes have been accredited by the Association are Aston, Warwick, Strathclyde (which pioneered the first distance learning MBA in the UK in 1983), Durham, Kingston and Leicester.
Henley's distance learning MBA students are encouraged to attend residential courses at the UK college or associate educational institutions abroad at the start of their studies, and regular subject and exam revision workshops thereafter. Henley pioneered the use of Lotus Notes, a form of information- sharing computer software that enables students and tutors to keep in touch with one another.
Peter Race, Henley's Director of distance learning programmes, says that distance learning is an increasingly popular mode of study because it offers students the flexibility to study when they want to without giving up core parts of their working weeks.
In October this year the college is launching a Flexible Evening MBA for City of London managers. This is a hybrid course - a cross between a part-time and a distance learning programme - involving the use of distance learning technology, self-study and face-to-face tuition.
Another provider of distance learning MBAs is Leicester University Management Centre. It has more than 2,000 students in the UK, South East Asia, the Arab Emirates, Spain and the USA, and it has set up 31 international resource centres recruiting students and marketing courses.
Patricia Greatorex, the centre's MBA Admissions Officer, says that Leicester's programme offers students with busy working lives the flexibility to fit their studies around their careers. The course, which can be taken in two to five years, requires a certain level of proficiency in the English Language, for example an IELTS score of 6.5 or TOEFL of 250 (600 in the old score).
Aston Business School has around 100 distance learning students. It offers part-time students the option of studying any module by attending lectures on campus or by watching videos of the course lectures at home.
Mark Oakley, the school's director of post graduate studies, says: "The distance learning mode appeals to people who are self-employed, or working in smaller businesses, who may not have the support of corporate employers to take time off to come and study at the campus.
"The one thing which you get with distance learning is flexibility. You haven't got to be at a university at six o' clock on Tuesday evening every week for 10 weeks. You can work around the materials."
Professor David Miles, dean of Kingston's business school, which has some 300 students on its open learning MBA in the UK and additional students in Moscow, Holland and Greece, explains Kingston's philosophy: "What we have tried to do is to design a programme which is attractive and accessible to busy mid-career professionals who do not have the time to take off the same period during every week to go to classes.
"We wanted to free them as much as we can from the constraints of timetables, recognising that they have got tight schedules and business targets to accomplish."
Kingston has tried to deliver the programme to suit the convenience of the student rather than the needs of the teacher. "We have proved to be very attractive to a particular type of student," he says. "The mid-career, highly active, very mobile professional attending high pressure events at work. Our MBA fits the rhythm of that kind of working life."