The British Horseracing Authority has refused to divulge

The British Horseracing Authority has refused to divulge how manyGodolphin horses have been tested for banned substances in the past two years, despite this week banning 15 of the stable's horses for six months and effectively casting the shamed trainer Mahmood al-Zaroonifrom the sport. 

While the BHA publishes figures showing how many raceday tests have been carried out in each calendar year, it said it would not break down the figures any further despite the shadow hanging over the world's biggest bloodstock operation.

It is understood that Certify, the winter favourite for the 1,000 Guineas who was one of 15 horses banned, after being given anabolic steroids by Zarooni, was tested twice last year and was clean both times.

The BHA also confirmed that both Godolphin yards in Newmarket – one under the aegis of Zarooni and the other under Saeed Bin Suroor – had been visited for "in training" testing in the past "few years" and no horses had tested positive.

The sport's governing body also said it was unrealistic to expect the winner of every race to be tested – hence it was inevitable that not every Godolphin winner would have been tested during the past two years. "We test horses from every race but not always the winner," said a BHA spokesman. "What I can say is that the winner of every major race almost certainly would have been tested."

The BHA's figures show that of 90,174 runners in 2012, it conducted 7,182 raceday tests – 14 of which were positive. It has pointed to those figures as evidence that racing does not have an endemic problem. Yet only 600-700 out-of-competition tests were carried out in 2012 as part of the BHA's "testing in training" sampling programme. Again, it would not break down where these tests were targeted.

"There could be a number of reasons why a yard could be idenitified for testing in training but we do not disclose the strategy for this," said the BHA.