August 2017: 'You never write the fact' - Salazar criticism frustrates Farah

Four-time Olympic champion Mo Farah has split from coach Alberto Salazar and will return to Britain.

Farah, who won 5,000m and 10,000m gold at London 2012 and Rio 2016, said his decision was based on a desire to move back to London.

Salazar is being investigated by the US Anti-Doping Agency (Usada) after BBC's Panorama made allegations about drugs use at his US training base.

"I'm moving back to London. I really miss home," said Farah, 34. external-link

He will now work with Gary Lough, who previously coached - and is married to - women's marathon world record holder Paula Radcliffe.

Salazar said he has offered to continue working with Farah in an advisory role.

'I'm not leaving because of doping claims' - why Farah is returning

Farah has been coached by Cuba-born American Salazar at the Nike Oregon Project camp since 2011, winning six world titles in addition to his four Olympic golds.

Both Farah and Salazar deny they have ever broken anti-doping rules.

"I am a firm believer in clean sport and I strongly believe that anyone who breaks the rules should be punished," Farah told the Sun. external-link

"I'm not leaving the Nike Oregon Project and Alberto Salazar because of the doping allegations.

"This situation has been going on for over two years, if I was going to leave because of that I would have done.

"If Alberto had crossed the line I would be out the door, but Usada has not charged him with anything. If I had ever had any reason to doubt Alberto, I would not have stood by him all this time."

Farah retired from track racing to concentrate on marathons after winning 10,000m gold and 5,000m silver at the World Championships in London in August.

He added: "I'm leaving simply because my family and I are moving back to London. We all loved spending our summer here and [Farah's wife] Tania and I realised how much we have missed spending time with our friends and family - and the kids are so happy here, too.

"We want the kids to grow up in the UK. It's the right thing to do for my family. But both Nike Oregon Project and Alberto are based in the USA, so it just would not be possible to continue our relationship from London."

Farah said new coach Lough "has an in-depth understanding of what is needed to achieve real results at marathon distance".

Salazar (centre) alongside Farah (right) and training partner Galen Rupp (left) at the London 2012 Olympics

Have claims tarnished Salazar and Farah?

Salazar, 59, has established himself as one of the world's leading coaches. But, in 2015, a BBC Panorama programme heard claims from former athletes at staff at the Nike Oregon projects about Salazar's alleged use of banned steroids and unethical practices.

Earlier this year, a leaked Usada report said Salazar "almost certainly" broke anti-doping rules over the infusion of a legal supplement. It also suggested he had failed to provide "acceptable justification for possessing testosterone".

Salazar, who has also worked as a consultant to UK Athletics, issued a 12,000-word open letter in 2015 denying accusations he had violated anti-doping rules.

Farah too has faced specific claims - in July he defended his record by saying he had "never failed a blood test" after hackers Fancy Bears revealed some of his samples had initially needed further testing, before later being declared normal.

The following month, after winning 5,000m silver and 10,000m gold at the World Championships in London, Farah was critical of sections of the media he said were trying to "destroy" his legacy.

Salazar has told The Oregonian external-link newspaper the decision to split was mutual and that he has offered to continue as an adviser to the Briton.

He added it made no sense for him to carry on as Farah's main coach from the US, with the runner focusing on a new discipline.

Analysis

BBC sports editor Dan Roan

Mo Farah is Britain's greatest track and field athlete, but also among the most controversial, thanks to his long association with Alberto Salazar.

For years he has been urged to distance himself from his controversial coach, and it will come as a relief to many that he finally has done.

Significantly however, the athlete has made clear that the doping allegations Salazar faces are not the reason for the split, and that he still stands by the coach. Indeed, Salazar has reportedly offered to work as an adviser to Farah so the links could continue.

This will not satisfy Farah's critics entirely: they will point to the athlete's relationship with another controversial coach, Jama Aden (arrested last year in connection with a doping inquiry), his two missed tests before the 2012 Olympics and documents leaked this summer in which he was named by an IAAF expert as "likely doping" before being cleared.

But many will see it as an important step.