Dubai's ruler has been cleared of any wrongdoing following a doping scandal at his Godolphin racing organisation that saw a trainer banned for eight years, an internal report said on Wednesday.

Sheikh Mohammed bin Rashid al-Maktoum, Dubai's ruler and the UK's leading racehorse owner, commissioned a report by Lord Stevens, the former Metropolitan Police chief commissioner, to investigate the scandal and interview key figures in the organisation.

Godolphin's former trainer Mahmood al-Zarooni was banned by the British Horseracing Authority (BHA) after being found guilty of administering anabolic steroids at his stables in Newmarket last year.

In unrelated incidents, veterinary goods described as "potentially toxic and dangerous to horses" were also taken from a private jet at Stansted Airport, while other unlicensed products were found at stables in Newmarket.

The BHA said in July the scandal, which caused serious embarrassment to Sheikh Mohammed, who is also Prime Minister of the United Arab Emirates, was a result of Zarooni acting alone without the knowledge of his senior staff, but an internal review was also ordered.

The report, which was completed through the global advisory firm Quest, confirmed the BHA's findings that Zarooni acted alone in procuring and transporting drugs to the UK, and that the seizures at Stansted and Moorley Farm were a result of management failings, insufficient oversight and complacency.

It also said there was no evidence of any link between the Zarooni case and the later seizures at Stansted Airport and Moorley Farm, and that the products seized were not illegal and are widely used and considered safe.

The report recommended the establishment of an internal compliance unit which will function independently of the horse training operation and have the power to examine any part of it and other internal units to ensure accountability and compliance.

"Although HH Sheikh Mohammed's equestrian operations are unusual in their size and scope, our review has highlighted the complexities of a regulatory framework that is a challenge for the entire equestrian industry," Lord Stevens said.

"Throughout our investigation of the three entirely separate incidents, we have established that no evidence whatsoever exists to suggest that HH Sheikh Mohammed had any knowledge of the purchase, transportation or use of any unregulated medicines. Equally neither did he have any knowledge of the illegal activities of Mahmood Al Zarooni."

Godolphin have won over 200 Group One races in different countries since Sheikh Mohammed established training operations in Dubai and England in 1992.-Reuters