Scientists have overcome certain difficulties in the technique of freezing of human eggs and have increased the chances of pregnancy to 34 per cent, which is on a par with what leading IVF clinics in Britain achieve with frozen embryos.

Experts said yesterday that the development could mean the practice of egg-banking is a viable option for single women who want to ensure they are able to start a family later in life.

The results also offer hope to thousands of female cancer sufferers who need to protect their fertility from the ravages of chemo-therapy and radiotherapy.

The research, published in the internet journal Reproductive Bio Medicine Online, follows warnings from Europe's fertility specialists that women need to start a family by their late twenties or risk remaining childless. However, the average age of first-time mothers has risen to 29, with many women not having a baby until their mid to late thirties.

Britain has 22 clinics licensed to store frozen eggs. Although the majority are for cancer patients, some cater for women in their twenties and early thirties who want to store their eggs in order to delay motherhood.

Human eggs can be frozen for more than a decade, but until now there has been little hope of using them successfully to have a child. Only 200 "ice babies" have been born worldwide. Britain's first frozen-egg baby, Emily Perry, was born in 2002 after her mother Helen was treated by the Midland Fertility Services clinic near Birmingham. Mrs Perry decided against creating and freezing embryos for religious reasons. A 36-year-old woman has recently given birth to "ice baby" twins after treatment at the same clinic.

Dr Simon Fishel, of the Care fertility centre in Nottingham, said: "At best, until now, we have been looking at just a 10 per cent success rate with egg-freezing, so this is a big step forward.

"In cases such as women with cancer where there is no other option it is worth freezing their eggs, but we have been discouraging egg-freezing for so-called 'social' reasons, because we just don't think it is viable. This research could change all that."

He added: "If it can be shown to be efficient and safe then you are looking at a social change. We would consider freezing and banking eggs for women for social reasons."

The new method of freezing eggs was developed by teams of doctors at Kato Ladies Clinic in Tokyo, the Danish Institute of Agricultural Science and the University of New Orleans. Following experiments using cows' eggs and the birth of several healthy calves, doctors attempted freezing and thawing human eggs.

While the eggs are freezing, they are susceptible to the formation of tiny ice crystals. These can tear and damage the eggs during thawing. Clinics usually store eggs in tiny plastic straws after using a solution to draw out moisture, in order to minimise the formation of ice crystals. The process is called vitrification. The eggs are then placed in liquid nitrogen to freeze them over three hours.

Under the new method, the Japanese scientists placed the egg in a vitrifying solution on a device called a Cryotop, which is a fine polypropylene strip attached to a plastic handle.

The device and egg were then plunged quickly into liquid nitrogen, a technique that further limits the formation of the potentially damaging ice crystals. When 64 of the stored eggs were thawed, 58, or 91 per cent, were found to be still healthy. Of these, 52 eggs were successfully fertilised and 32 then developed into healthy embryos.

A total of 29 were transferred into female patients, including cancer survivors, with an average age of 32. Seven healthy babies were born as a result of treatment and three women still have on-going, healthy pregnancies.

The pregnancy rate per embryo transfer was 34 per cent, which is as good as that seen at the best IVF clinics in the country using frozen embryos.

Embryologist Virginia Bolton, of King's College Hospital in South London, said: "If these figures can be borne out through other research it will be very promising.

"If you can get a pregnancy rate of 30 to 40 per cent per embryo transfer then you are doing really well. That is what we see in the best units using frozen embryos, but this is using eggs, which are notoriously difficult."

Source