TEAM SKY, whose riders Sir Bradley Wiggins and Chris Froome have claimed the past two Tour de France titles, has been plunged into controversy after one of its cyclists was asked to explain suspect variations in blood readings.

Jonathan Tiernan-Locke, 28, from Plymouth, who won last year’s Tour of Britain, has received a letter from the UCI, cycling’s governing body, after the discovery of irregular variations dating back to September 2012, three months before he joined Team Sky. He has three weeks to provide an explanation.

The variations do not mean Tiernan-Locke is guilty of doping or any other illegal practice. However, the biological passport, in which they were detected, is regarded as a key tool in helping authorities uncover the use of banned substances.