The British world road cycling champion was suspended on 11 July pending disciplinary action but appealed to the Court of Arbitration for Sport (Cas).

She successfully argued the first of the tests should be declared void.

UK Anti-Doping (Ukad) says Armitstead, 27, did not challenge the validity of the first two missed tests at the time.

Armitstead told the Daily Mail: "I did think about it [challenging the first 'failure'].

"The reason I didn't was because it was my first strike and it was very close to the World Championships, so I was travelling to America.

"I also didn't have the legal advice. It felt very much them against me. I was very naive. I went ahead to the World Championships and I didn't want the distraction."

In a statement, Ukad chief executive Nicole Sapstead said it respected the outcome of the Cas hearing but wanted to know the "reasoned decision" why the first test failure was not upheld.

Speaking to BBC Radio 5 live, Sapstead added: "I'd like to think that we are a reasonable organisation and we don't bring cases against athletes unless we see reason for doing so."

Armitstead was Britain's first medallist of London 2012 with silver in the road race and is one of the favourites for the same event in Rio on Sunday.

She admitted the prospect of being banned had left her feeling like she was "standing on the edge of a cliff", adding: "I was more concerned about my reputation and people's understanding of it.

"I could have been banned. That's what I was most scared about. All the hard work being for nothing.

"The hardest thing about this situation is that there will be people who will always have doubts about my performances."

Armitstead won the world title in Richmond, in the United States, last September.

The news of Armitstead's missed tests was revealed by the Daily Mail, which said she was supported by a legal team funded by British Cycling.

However, a British Cycling statement said: "We paid for legal advice on our own position because there were a number of considerations as she was going through the Olympic selection process and was a podium athlete.

"That legal advice was shared with Lizzie and her team. Lizzie herself funded the actual appeal to Cas."

Reaction

Great Britain's Nicole Cooke, the road race champion at Beijing 2008 said the drug-testing system "does allow for athletes to notify the testing authorities either by sending a text message or ringing a hotline up to one minute before the one-hour window opens and changing it".

Cooke and Armitstead, team-mates at the London Olympics, were involved in a fallout at the 2011 World Championships after Cooke rode on when Armitstead crashed.

"In 14 years of tests I have one recorded missed out of competition test," added Cooke. "Fair rules to be applied fairly, at all times, to all athletes."

Armistead's reprieve has also caused some concern amongst other Olympians.

British rower Zac Purchase, who won Olympic gold in 2008, said British Cycling and the Armistead camp were guilty of a "monumental cock-up".

He added on social media: "Imagine what we would be saying if she was Russian... #NotWorthIt #KeepSportClean."

Canadian three-time Olympian cross-country mountain biker Geoff Kabush also posted on social media. He said: "1st test understandable but I'd be hyper aware about missing 2nd. If I missed 2nd there is no chance I'd miss 3rd???

"So many questions. How is World Champ suspended for 3 weeks and no one knows?"

What British cyclists are saying

Britain's first three-time Tour de France winner Chris Froome: "I think the rules are there and the authorities are the ones with the information to make these decisions.

"This is one for the authorities and you have to hope they make the right decision."

Double Olympic gold medallist Geraint Thomas: "It's tough - we all do it [testing], we all have to.

"With such a hectic race schedule you do make mistakes - but I was surprised when I saw the news.

"It's difficult for her. I fully think that Lizzie is a clean athlete, I've got no doubts about that."

Background

Athletes must make themselves available for testing for one hour each day and inform testers of their location.

Had Armitstead been found to have missed three tests in less than a year, she would have violated the World Anti-Doping Agency's code and faced a ban of up to two years.

A statement on Armitstead's behalf said she was charged by Ukad on 11 July with three so-called 'whereabouts' failures, leading to a suspension pending disciplinary action.

The first came at a World Cup event in Sweden on 20 August, 2015.

The second was "an administrative failure" by her on 5 October.

And the third was a missed test on 9 June this year following "an emergency change of plans due to a serious illness within her family".

Armitstead did not dispute the second two faults, but successfully appealed to Cas over the first missed test, which happened at a team hotel in Sweden.

She undertook in-competition testing the following day, as leader of the UCI Women Road World Cup.

"Cas ruled the Ukad doping control officer had not followed required procedures nor made reasonable attempts to locate Armitstead," the statement added.

"Cas also ruled that there was no negligence on Armitstead's part and that she had followed procedures according to the guidelines."

(BBC)