This was revealed last week when a Russian-based group of computer hackers known as the Fancy Bears started to publish private medical data belonging to some of the world's leading athletes that they stole from the World Anti-Doping Agency.

In a pre-recorded interview with BBC1's Andrew Marr Show that will be broadcast on Sunday morning, the 36-year-old rider said: "(The triamcinolone) was prescribed for allergies and respiratory problems.

"I've been a life-long sufferer of asthma and I went to my team doctor at the time and we went, in turn, to a specialist to see if there's anything else we could do to cure these problems.

"And he said 'yeah, there's something you can do but you're going to need authorisation from cycling's governing body'.

"You have to show and provide evidence from a specialist that they will then scrutinise with three independent doctors and authorise you to take this product. If one of those three doctors says no, you get declined.

"This was to cure a medical condition. This wasn't about trying to find a way to gain an unfair advantage.

"This was about putting myself back on a level playing-field in order to compete at the highest level."

The authorisation Wiggins refers to is known as a therapeutic use exemption (TUE), which is effectively a doctor's note allowing an athlete to use a substance that would normally be prohibited under WADA's rules because of its performance-enhancing qualities.

After last week's Fancy Bears leak, it is now known that Wiggins has received six TUEs during his career: three for asthma inhalers between 2008 and 2009, and the three injections between 2011 and 2013.

The five-time Olympic champion still uses an inhaler but no longer needs a TUE to cover that as WADA relaxed the rules for the most common asthma drugs in 2010. But triamcinolone, a corticosteroid, remains banned as it can aid recovery from strenuous activity, postpone fatigue and help with weight loss.

However, there is no suggestion that either Wiggins or Team Sky, his former team, have broken any rules, and his TUEs were approved by the British authorities and cycling's world governing body the UCI.

Team Sky responded to the publication of Wiggins' TUEs by saying it had followed the rules to the letter and restating its commitment to clean sport. British Cycling has said it is "proud of its strong anti-doping culture".

But that has not stopped several current and former riders from criticising Wiggins and Team Sky for seeking permission to use the drug on the eve of his main target in each of those seasons, and expressing surprise that the authorities allowed them to do so.

Germany's Jorg Jaksche told the Cycling Tips website that he and his team-mates used the drug illegally a decade ago and branded Team Sky as "a bunch of hypocrites", while Britain's David Millar told the Daily Telegraph it was "the most potent" drug he used when he was doping and "could not fathom" why a doctor would have prescribed it so close to a race.

On Friday, the BBC's Newsnight broadcast an interview with the doctor from the team Wiggins was riding for (Garmin-Slipstream) when he finished third in the 2009 Tour de France, his breakthrough performance on the road.

"I was surprised to see there were TUEs documented for intramuscular triamcinolone just before three major events," said Dr Prentice Steffen, a well-respected figure within the sport.

"You do have to think it is kind of coincidental that a big dose of intramuscular long-acting corticosteroids would be needed at that exact time before the most important race of the season.

"I would say certainly now in retrospect it doesn't look good, it doesn't look right from a health or sporting perspective."

Wiggins, though, told the Andrew Marr Show he needed the drug to combat a serious allergy to pollen that would exacerbate his asthma.

When asked how he could justify taking a drug usually prescribed for acute asthma attacks less than a week before the Tour, and just two weeks after winning the Criterium du Dauphine, Wiggins said: "June-July is the worst period for that - April, June, July, right through those months - and I was having problems.

"When you win the race three weeks out from the Tour de France, as I did, you're the favourite for the Tour.

"(And) you have the medical team and coaches checking everything's OK - 'Bradley, you're on track here, you're the favourite to win this race, now we need to make sure the next three weeks is...is there anything we can help with at the moment?'

"'Well, I'm still struggling with this breathing, I know it didn't look like it but is there anything else you can do just to make sure that I don't, this doesn't become an issue into a three-week race at the height of the season?'

"And, in turn, I took that medical advice (to take triamcinolone)."

Wiggins will hope this interview draws a line under a difficult chapter in what has been an otherwise magnificent story for him as an athlete, particularly as he is widely expected to retire as a professional rider at the end of this season.

But that will not stop this debate rumbling on within the sport, as Dutch rider Tom Dumoulin, one of cycling's rising stars, told the De Limburger newspaper on Saturday that he thinks the whole episode "stinks".