Police appealed to the public for help last weekend when terror suspect Mohammed Ahmed Mohamed -- who was subject to a "terrorism prevention and investigation measure," or TPIM -- tore off an electronic surveillance device and slipped out of a London mosque disguised in a burqa.
Mohamed, suspected of aiding the Somali terrorist group al-Shabaab, was the second such suspect under a TPIM to flee in within a year. Ibrahim Magag, also thought to have links to the Somali group, disappeared in December.
A manhunt was under way for Mohamed Tuesday when London's popular mayor sharply criticized the government's use of TPIMs as an anti-terrorism tool, saying the 2-year-old strategy was failing to keep the country safe.
"Plainly they are not working in the way we would like them to work in the sense that this guy Mohamed was able to flee in absurd circumstances and there must be questions about whether we should be tougher in the way we administer these things," he told Britain's LBC 97.3 radio station.
"If a fellow can get into a burqa and evade his invigilators in the way that Mr. Mohamed has done, then we clearly need to look at how it is working. Depending on how much of a risk you are deemed to pose, you should be deprived of contact with networks that might help you with any end you desire."
The TPIM regime was instituted in 2011 after Britain's controversial former policy of using "control orders" to forcibly relocate terror suspects ran into legal problems. A series of courts rulings determined they violated the human rights of suspects.
In a compromise hammered out between the Conservative Party and Liberal Democratic government coalition partners, the TPIM system was put in place, under which suspects are required to wear an electronic ankle tag with and report daily to the police for a two-year period.
They also must meet other requirements limiting their travel, where they can live and with whom they can associate.
Mohamed, one of nine people in Britain currently subject to a TPIM, isn't considered a "direct threat" by police, Home Secretary Theresa May told Parliament Monday while defending the anti-terror measures.
"Even if we wanted to go back to the days of control orders, we would not be able to do so," she said, adding, "The police and the security services have always said that there has been no substantial risk since the introduction of TPIMs."
But Johnson, a Tory who is one of the most popular political figures in the country, blamed "coalition politics" for weakening Britain's anti-terrorism efforts, urging May to "get tough" with Liberal Democrats on the issue.
"Characters such as [Mohamed] -- and even if he doesn't pose an immediate threat to this country, it is plain he is a danger -- should be more closely invigilated than they currently are and I am sure that is a point that Theresa May will be taking up," he said.
Aides to Liberal Democratic leader Nick Clegg have strongly denied the party weakened anti-terrorism legislation in negotiations with Tory coalition partners, the London Evening Herald reported.