Evidence given by Sir Dave Brailsford in Bradley Wiggins mystery medical package case 'extraordinary' says UK anti-doping

He questioned why specific details – such as the time the package was delivered – could be recalled yet no-one could remember what was in it.

And he also warned: “We’re not giving up on this, and we'll dig and delve and find out what was in that package.”

The controversy was triggered by revelations a medical package had been delivered from Team Sky’s Manchester headquarters to a Team Sky doctor for Wiggins at a race in France 2011, which he won.

In December, the Sky team boss Sir Dave Brailsford told MPs on the House of Commons’ Culture, Media and Sport Select Committee that the package contained a legal decongestant called Fluimucil.

However this prompted questions over why the medicine had to be delivered all the way from the UK rather than being sourced locally.

When asked about this explanation given by Brailsford, Kenworthy - who will soon be stepping down from his role at UKAD, - said: “Well that’s what Dave Brailsford came out with at the hearing. But actually, if you recall, he didn't say: 'I know that's what it was'. He said: 'I have been told that's what it was'.”

Bob Howden, the president of governing body British Cycling told the MPs he did not know what was in the package, which was delivered by a coach employed by British Cycling at that time. The coach, Simon Cope, has previously said he did not “have a clue” what the Jiffy Bag parcel contained.

Brailsford said to MPs that documentary evidence of the medication would be supplied and Wiggins’ medical records had been provided to UKAD to back up his explanation.

But Kenworthy said: "There's still no definite answer from anyone who was involved. I still don't know what was in there; I'm no nearer finding out than you are.

"People could remember a package that was delivered to France, they can remember who asked for it, they can remember the route it took, who delivered it, the times it arrived. The select committee has got expense sheets and travel documents.

"So everybody can remember this from five years ago, but no-one can remember what was in the package. That strikes me as being extraordinary. It is very disappointing."

On the issue of whether British Cycling should have kept records of the medication taken abroad, Kenworthy said “one would think so”.

He added: “Here's an individual [Cope] who's carrying a package containing medicine across international boundaries, and he's no idea what's in them.

"One could say he could be putting himself at risk if they are drugs which one could not properly transport. Someone should be inquisitive enough to say: 'Well what is it I'm actually taking?'."

Five-time Olympic champion Wiggins, who announced his retirement last month, has been under increased scrutiny since details of his therapeutic use exemptions (TUE) – which authorises athletes to take a prohibited drug for legitimate medical reasons - were leaked by Russian computer hackers. While there is no suggestion he broke anti-doping regulations, it emerged he was given TUEs to take an anti-inflammatory drug before three races: the 2011 and 2012 Tour de France and the 2013 Giro d'Italia.

Kenworthy said the case of the mystery medical package was something that had “undermined yet again the joy of sport” and cast a shadow over Wiggin's departure from the sport.

He said: “One of the tragedies of all this is you've got probably one of the greatest cyclists that the UK has produced, who's just coming to his retirement, and all the talk is not about the successes that he's had, but about this package.”

British Cycling said it could not comment while the UKAD investigation is ongoing. Team Sky said it was confident there had been no wrongdoing and they were co-operating fully with UKAD.

Last week it was announced Wiggins will be one of the contestants on the new series of Channel 4’s reality winter sports show The Jump.