Though the medical potential of umbilical cord blood has long intrigued doctors and scientists, most have a low opinion of private companies that offer parents the chance to bank stem cells when babies are born.

The banking services, which are already offered by seven companies in the UK, are usually marketed as personalised “spare part” kits that could be used to treat diseases such as leukaemia, but experts say the chances that any child will ever need one are vanishingly small.

Even if a child were to develop one of the 75 rare blood or immune system disorders that can be treated with cord blood, he or she would be much more likely to need stem cells from a donor. Stem cells from its own cord blood would be genetically identical to the patient, and thus risk reintroducing the disease.

While it might be possible to grow other replacement tissues from cord blood cells in the future, this prospect remains distant and unproven. Some scientists think it disingenous to persuade patients to pay out large sums for the sake of such an uncertain benefit.

Obstetricians and midwives are also concerned that extracting cord blood immediately after birth would place an excessive burden on medical staff who are already overstretched, at a critical moment for the health of mother and child.

Sir Richard Branson’s Virgin Health Bank addresses some of these concerns but by no means all of them.

It is genuinely innovative, in that the cord blood it collects will be split into two, 20 per cent of which will be stored for the family’s exclusive use, and 80 per cent placed in a public bank.

This has been welcomed by doctors and scientists, as large public banks containing stem cells of multiple tissue types will be of much greater benefit to patients. Children are much more likely to need tissue from the public bank than their own privately stored stem cells — and Virgin has been commendably explicit in telling potential clients that there is a very low chance that their private supplies will ever be needed.

Sir Richard, however, pledged yesterday that blood from the public bank would be available free to anyone who needs it, which raises the question of why parents would want to pay £1,500 to be involved. Their children stand to benefit only if it becomes possible in the future to use their personal stem cell stocks in regenerative medicine.

What the Virgin model does not resolve, however, is the collection issue — the chief concern for many professionals. Though Virgin considered employing third parties to collect the stem cells, it has not ultimately done so, preferring to rely on the goodwill of doctors and midwives.

This is highly unlikely to be forthcoming. There is a serious shortage of NHS midwives, who must often care for two or three women at once, and it is unrealistic to expect them to devote extra time to taking cord blood for paying customers.

Unless Virgin pays for midwives of its own, or other third parties to collect the blood, it is hard to see many NHS hospitals offering its service.

Virgin’s publicity material has also given a somewhat misleading impression of what will happen to any profits from the project. While Virgin has announced that it will donate all its profits to research into cord blood stem cells, it has kept quiet about the fact that its partner, Merlin Biosciences, has a 50 per cent stake and will keep its share of any profits.

While the initiative is clearly not as nakedly commercial as those of its market rivals, it is not quite as charitable as it might at first seem.

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