In an interview with The Telegraph, Mr Johnson warned that David Cameron’s “emergency brake” on migrant benefits will do nothing to reduce the numbers of foreigners coming to the UK.
In his first detailed comments since announcing that he was backing a “Brexit”, the Mayor of London hailed the "extraordinary" response of Eurosceptic MPs and said he will try to encourage ministers to change their mind and back the out campaign.
Theresa May, the Home Secretary, and Sajid Javid, the Business Secretary, both refused to back a Brexit despite being life-long Eurosceptics.
Asked whether Cabinet ministers should now reconsider their decision to support the “Remain” campaign, Mr Johnson said: “What have we got? About 150 MPs now? That’s extraordinary.
“I would [encourage ministers to think again]. People should look at the arguments. I have huge respect for what the Prime Minister is saying. But people I think should think about the arguments.”
Mr Johnson also attacked Mr Cameron’s deal from Brussels on migrant benefits after official figures showed that net migration reached 323,000 last year, close to record levels.The Prime Minister has hailed his offer of a four-year "emergency brake" on benefits and suggested that it will reduce the "pull factors" for EU migrants.
However, critics have warned that it will have little effect because it is tapered, meaning that migrants gradually gain more access to Britain's benefits system the longer they stay in the UK.
Asked whether Mr Cameron’s “emergency brake” on migrant benefits will “work and reduce the numbers”, Mr Johnson said: “It seems unlikely frankly.”
He added: “This is about control. People feel a sense of alienation and frustration because the politicians have no control.”