Floyd Landis has launched a stinging attack on Team Sky, claiming the idea of marginal gains and a zero tolerance policy is a facade and just great PR. The former American rider who turned informant after testing positive for drugs himself scoffed at possible explanations for Chris Froomes failed test and expects the fallout to be a death knell for Team Sky after eight years at the top.

Former US Postal Service rider Landis, who won the Tour de France in 2006 before being told of a positive test for testosterone 72 hours later, contributed to the downfall of Lance Armstrong with his testimony of widespread doping in cycling.

He fears history is repeating itself in the peloton, a theory he claims is supported by Froomes recent adverse test. Both Froome and Team Sky deny breaking any anti-doping rules and are seeking to explain why the four-time Tour de France winner had twice the legal level of asthma drug salbutamol in a urine test during his Vuelta a Espaa victory in September last year.

The appeal process is expected to take at least a few more months. One possible explanation Team Sky may seek to support is that Froomes adverse test was the result of too many puffs on his inhaler after the race. Another is that a kidney malfunction meant the 32-year-old secreted salbutamol before releasing large quantities immediately before the drugs test. But Landis has no doubt that it will eventually lead to a ban.

There is evidence that salbutamol can be performance enhancing if its used orally or intramuscularly, said Landis. Its very difficult to get to the level that Chris Froome showed by using an inhaler. If that will form his excuse I think its nonsense and I dont think many buy it. Hes trying to defend himself because he has everything to lose. I feel sympathy for him but if he doesnt face it now he will have to later.

Team Sky was founded after decades of doping left the reputation of professional cycling in tatters. But doubts have formed around Dave Brailsfords team with Froomes failed test, which came to light following a joint investigation between the Guardian and French newspaper Le Monde. They were already fighting scepticism inflicted by the mystery of a jiffy bag delivered to Bradley Wiggins at the Critrium du Dauphin in 2011 and more recently with the former Team Sky coach Shane Suttons claim that he viewed Therapeutic Use Exemptions as a legitimate means to find a gain. There was also an alleged delivery of banned testosterone patches to the Manchester velodrome addressed to Doctor Richard Freeman, who was employed by Team Sky in 2011, which the medic claimed was sent by a supplier in error.

Landis does not conceal his amusement. Sometimes random or coincidental things happen but Ive got to be honest, he laughed, I find it very very hard to believe that a package of testosterone was accidentally mailed to a velodrome.

We can take from what Shane has said they were at least pushing the limit with certain things and now with Froomes failed test, he added, if you take all those things together, theres no defending that team. Any reasonable person would have more questions.

Theres no belief in that zero tolerance system any more; that was never a real thing it was just great PR about marginal gains and all these cute little sayings they thought up.

Landis, 42, now lives predominantly in Colorado, USA where recreational cannabis was legalised in 2012. He is out of cycling and owns a company, Floyds of Leadville which retails marijuana and marijuana-infused products. But he played a major part in Armstrong, his team-mate at US Postal, becoming one of the worlds most acclaimed athletes.

For four years after failing a drugs test Landis protested his innocence before becoming a whistleblower for a US Anti-Doping Agency investigation led by Travis Tygart. But Landis feels the authorities have no real appetite for catching the cheats.

Travis assured me that his objective was to figure out the anti-doping system and eliminate the guys running the sport but that wasnt done, said Landis. They were protected.

Wada is designed to protect the Olympic committee, he added, theyre not designed to catch people using PEDs and here we are again. Its been 11 years but the one thing that bothers me is I went through all that and accomplished nothing. I think Lance feels the same way and he has a right to. If youre going to take us out and say these guys are the bad guys, you cant just sit back on your hands and let things return to exactly the way it was.

Froome has already committed to riding in the Giro dItalia in May as he seeks to add another Grand Tour victory to the collection. But Landis expects the Briton to be convicted of an anti-doping rule violation and serve a ban. If this scenario unfolds he thinks it will spell the end for Team Sky.

When you have someone that high profile who suffers a ban it usually means the whole thing implodes, said Landis, If I was on the board of directors or an executive at Sky or any of the companies who sponsor them I would be long gone. At some point they have to make a decision that looks ethical.