Weakened security laws allowed a suspected terrorist to get close to the venue for the Olympic Games five times in recent months, Labour has said.
Shadow home secretary Yvette Cooper demanded to know whether the incidents posed a threat to London 2012 safety and pointed the finger at watered-down Government anti-terror measures.
Court papers show that the 24-year-old, known as CF, was arrested and faces criminal proceedings after the authorities found he took trains through the Olympic Park despite being banned from the area.
His movements were picked up because he has to wear an electronic tag as part of restrictions imposed on him by an order under the Terrorism Prevention and Investigation Measures Act - referred to as a "Tpim".
CF's lawyers insist that he only used the route to visit a solicitor dealing with his legal challenge against the order - due to be heard by the High Court on Monday - and had been wrongly advised that was OK.
But Labour said the fact that he was able to be in the capital at all - after being ordered under the previous anti-terror regime to stay out of the capital altogether - highlighted a serious problem.
Tpims replaced the control orders system previously used to restrict the movements and contacts of individuals thought to pose a risk to the public but who cannot be tried for reasons of national security.
Under the new regime the coalition stripped authorities of the right to forcibly relocate suspects, a power which had been opposed by the Liberal Democrats. The Home Secretary has since proposed reserve powers that would enable enforced relocation in exceptional circumstances - but they would need parliamentary approval. Experts, including the Government's independent reviewer of terror laws, had called for the relocation powers to be retained at least until after the Olympics.
High Court papers show CF's legal team have promised written evidence to prove he was seeing his solicitor on each occasion. They blame the breach on "erroneous advice" given by the solicitor that the London Overground journeys were not in breach of the Tpim because they did not involve him stopping at Stratford International station.
CF was held overnight after being arrested for entering the Olympic no-go zone but was subsequently released on bail and is due to face prosecution for the breaches later this month.