The headquarters of British Cycling were visited by officials from UK Anti-Doping (UKAD) on Friday 7 October. The visit took place amidst ongoing speculation about the use of banned substances by a number of high profile athletes, including Sir Bradley Wiggins, under a Therapeutic Use Exemption (TUE) issued by the World Anti-Doping Agency (WADA).

Though some reports suggested a raid had taken place at the National Cycling Centre in Manchester, UKAD said the visit took place with British Cycling's "full cooperation". According to the BBC, UKAD confirmed the investigation but said to "protect the [investigation's] integrity" it would not comment further.

The investigation follows comments made by former Team-Sky rider Jonathan Tiernan-Locke, who told the BBC this week that painkillers including Tramadol – an opioid used to treat moderate to severe pain – were made "freely available" to riders by Team Sky at the 2012 World Road Championships. According to the BBC, the medic responsible denies this.

Tiernan-Locke, who recently served a two-year ban after tests revealed a discrepancy in his biological passport data leading to suspicion of the use of blood-boosting drugs, said the Tramadol use "didn't sit comfortably" with him.

He said: ""I wasn't in any pain, so I didn't need to take [Tramadol]."

A report by the Daily Mail last week also alleged that a medical package had been delivered to Team Sky by a British Cycling coach in 2011 ahead of Wiggins' Criterium du Dauphine victory. However, Team Sky said it had conducted a review and concluded there had been no wrongdoing.

"We informed British Cycling of the allegation and asked them to contact UKAD, who we will continue to liaise with," said Team Sky.

British Cycling, whose riders including Wiggins, Chris Froome, and couple Laura Trott and Jason Kenny, was the subject of speculation by other countries following another bumper medal haul at the Rio Olympics this summer. It said in a statement it was "cooperating fully" with the investigation.

Doubt was first cast on Team Sky after hacking group Fancy Bears leaked details of eight-time Olympic medallist Wiggins' use of a TUE which permitted intra-muscular injections of corticosteroid Triamcinolone, which is on WADA's banned-substance list. In the documents on Fancy Bears' website, it shows that Wiggins used the drug before several major races including the 2012 Tour de France, which he won while riding for Team Sky.

Though there is no question as to whether Wiggins broke the rules, having obtained the exemption from WADA for allergy relief associated with asthma of which Wiggins is a life-long sufferer, several athletes have claimed the TUE system is open to abuse. Earlier this week, former Sky rider Tiernan-Locke said the timing of the TUE was suspicious.

Tiernan-Locke told the BBC: "From the outside it definitely looks odd that you would apply for a TUE before the three major grand tours, but then again he's just following a process... If he's got allergies maybe they're [his medical team] suggesting that's the best way round it."

A number of the athletes whose details were leaked by Fancy Bears detailed use of drugs associated with asthma. Tiernan-Locke also expressed scepticism about this with regards to cycling, questioning how it was possible that so many cyclists suffered from such similar respiratory problems.

Sir Bradley Wiggins
Sir Bradley Wiggins received an intra-muscular injection of Triamcinolone before his 2012 Tour de France victory Getty Images