The chief executive of UK Anti-Doping says not hearing the doorbell is not a good enough reason for missing a drugs test.

The Daily Mail alleges Mo Farah missed two tests in the lead up to London 2012, including one where it is claimed that he did not hear testers who turned up to his house.

UKAD CEO Nicole Sapstead says athletes need to be alert.

"Simply saying that you forgot or that you didn't hear is not an acceptable excuse," she said. 

The double Olympic champion's coach Alberto Salazar and his training partner Galen Rupp have denied recent allegations of doping while Farah is not suspected of wrong-doing.