Drug cheating allegations are casting a shadow on Britain's greatest Olympian - but the runner is fighting back.

Gold medalist Mo Farrah claims he's clean after British media leaked a report revealing his coach, Alberto Salazar, had given drugs to some of his athletes without justifiable reason.

The report doesn't specifically link to Farrah - but UK correspondent Gavin Grey told Rachel Smalley it's causing problems for Britain's golden boy.

"There is no naming of Mo Farrah as one of those athletes but it casts that shadow on what otherwise is a completely unblemished career."