London Marathon organisers say they are “very concerned” following allegations that the race was won seven times in 12 years by athletes who recorded abnormal blood scores, suggesting some may have doped to secure victory in the prestigious event.

Fresh revelations from the Sunday Times claim the suspicious results, which constitute almost 30 per cent of winners in the men's and women's London Marathon races between 2001 and 2012, were a combination of tests carried out at the time of competition and at other points during the careers of the athletes in question.

At a time when athletics has been dogged by numerous allegations of widespread and endemic doping, these latest claims - which have emerged following a leaked International Association of Athletics Federations database of 12,000 blood tests from 5,000 athletes – put the sport under the spotlight once again just weeks before the World Championships in Beijing.

Analysis by the scientists Robin Parisotto and Michael Ashenden of the top three finishers at each of the world marathon majors – in London, Boston, New York, Chicago, Tokyo and Berlin – found that in London seven race winners, six runners-up and seven third-placed finishers gave abnormal blood samples over the period.

It is claimed that 34 winners of those major marathons should have faced censure or been investigated over potential blood doping, while those athletes whose samples were deemed suspicious collected more than £3 million in prize money. Blood doping is the process of increasing the number of red blood cells in the body to significantly enhance performance, although these allegations do not prove the existence of the practice.

Nick Bitel, the chief executive of the London Marathon, criticised the IAAF and said marathon organisers do not see the results of drug tests undertaken at the event despite paying for the programme. "We are disappointed," he said. "We're doing more than anybody else to fight doping in our sport. What this story is really about is the IAAF's failure to take effective action."

A London Marathon statement read: “We believe there are people in our sport who are cheating and everyone has a part to play to protect those who are not. We continue to be at the forefront of anti-doping measures for marathon runners as we are determined to make marathon running a safe haven from doping but we cannot do it all on our own and rely heavily on the IAAF.

"We are therefore very concerned by the allegations made in the Sunday Times today and we will be discussing the implications of the allegations with the IAAF. The London Marathon does not see the results of the tests and is therefore only informed if there is an adverse result from a test carried out at the London Marathon. We have never been informed of an adverse test from an athlete tested at the London Marathon between 2001 and 2012, or subsequently."

An IAAF spokesman said: “All the marathon organisers had a thorough explanation of what the ABP [athlete biological passport] was when the IAAF engaged in joint blood testing with them. In four years of cooperation they have never asked to see any results. The London Marathon do not pay for all the testing. It is a joint programme of London Marathon/IAAF and UKAD [UK Anti-doping] is used to collect the samples.”

The World Anti-doping Agency has already announced it will launch an urgent investigation into allegations of widespread doping in athletics after allegations last week that more than 800 athletes had suspicious blood results that were not followed up by the IAAF. The governing body described the claims as "sensationalist and confusing" while Lord Coe, an IAAF vice-president who is running for the organisation's presidency, described the accusations as

“a declaration of war on my sport”

Mo Farah, whose American coach Alberto Salazar has been at the centre of doping allegations, is one of eight British athletes who have asked for their blood test data to be made public by the Sunday Times. It reported that 20 of Farah's results from the IAAF database between 2005 and 2012 were within the normal range, the double Olympic champion saying: "I'm happy to do what it takes to prove I'm a clean athlete."

On Thursday Russia’s Liliya Shobukhova was stripped of her London and Chicago marathon titles after all her results since 2009 were annulled and a doping ban extended by 14 months. Shobukhova won the London Marathon in 2010 and finished second the following year before irregularities were discovered in her biological passport.