Women undergoing fertility treatment have had their eggs fertilised with the wrong sperm in a series of mix-ups at one of Britain’s most famous hospitals.

Embryos belonging to three couples had to be destroyed and their cycles of treatment abandoned after the errors were discovered at Guy’s and St Thomas’ hospital in London earlier this year.

In a separate blunder, a woman had the wrong embryo implanted at the same hospital in 2007.

Fertility experts say the errors, along with similar mistakes at other hospitals, raise serious concerns about the way IVF clinics are regulated. They believe the Human Fertilisation and Embryology Authority (HFEA), the watchdog, is failing to deal with serious problems.

The mistakes have raised concerns about a “casual approach” to the 37,000 British couples who seek fertility treatment every year.

Critics point out that inspection reports from 2007 and 2008 warned that Guy’s and St Thomas’ was carrying out risky procedures in the preparation of sperm samples for fertilisation.

A February 2007 report by the HFEA warned that embryologists at the hospital were running the risk of confusing sperm samples from different men by preparing them in the same container. Yet errors were still being made earlier this year.

One of the recent cases was discovered when the embryologist realised she had used a sample from the wrong man to fertilise a patient’s eggs.

Within days of this mistake, scientists carrying out tests designed to ensure that babies are free of hereditary diseases found genes showing that the embryos could not belong to the parents they had believed to be the owners.

In 2007 a patient at Guy’s had been implanted with the wrong embryo. The treatment failed to result in a birth and embryologists later discovered that they had put back a weak embryo – despite the patient having created a stronger one that had a greater chance of developing into a baby.

Documents seen by The Sunday Times show a series of mistakes at other clinics that led to general warnings being issued.

In one incident, a surrogate mother was given embryos from a couple who had a similar-sounding surname to the couple who had hired her. The surrogate did not become pregnant. The HFEA warned clinics about the mistake in March 2007, but the incident was not made public.

At another unidentified clinic, a woman became pregnant after she was implanted with embryos belonging to another couple with the same surname. The HFEA told clinics about the mix-up in May 2007 but the public was again not informed. The pregnancy ended in miscarriage. At about the same time, treatment for two other couples had to be abandoned after their embryos were mixed-up.

Josephine Quintavalle of the campaign group Comment on Reproductive Ethics, said: “It is horrifying that this information is not available to the public. I didn’t realise the extent of this. The casualness is just dreadful.”

Sue Avery, consultant embryologist at Birmingham women’s hospital and a former chairwoman of the Association of Clinical Embryologists, said the sperm mix-ups at Guy’s were “very serious”. She said it was disappointing that clinics had not learnt lessons from the mistakes that had led to the birth of black twins to a white couple in Leeds in 2002.

Despite the repeated mistakes at Guy’s and St Thomas’ hospital, the HFEA has not carried out an investigation.

Avery said: “We would expect in the case of repetition that the HFEA might want to investigate unless they can be thoroughly satisfied that the centre has taken sufficient action.”

The assisted conception unit at Guy’s and St Thomas’ hospital said a thorough internal investigation had been carried out and the HFEA was informed of the mistakes.

The HFEA said that while IVF was a delicate procedure and it was impossible to eliminate human error, only 0.5% of treatments resulted in problems.

It added: “The HFEA takes incidents very seriously. When incidents are reported to us, we will investigate and take action where necessary. The risk of mix-ups is a serious concern for patients, clinics and the HFEA.”

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