Mayor of London Boris Johnson on Saturday urged British government ministers to join referendum campaign to leave the European Union on June 23.
"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," he told the Telegraph newspaper in an interview.
Johnson recently ditched British Prime Minister David Cameron’s call to stay in the European Union and said that he backed the so-called Brexit.
The UK will hold a referendum on June 23 to decide whether it remains part of the EU.
In a separate interview with the Times newspaper, Johnson dismissed the argument that a "leave" vote could spark last-ditch talks to achieve a better settlement for Britain inside the EU, resulting in a second referendum.
Asked whether there could be another referendum, Johnson told the paper "No. Out is out."
He said that recent reforms Cameron secured to welfare payments to EU workers seemed "unlikely, frankly" to reduce the numbers of new arrivals as the premier had argued.
Johnson, told the Daily Telegraph that he was "massively pro-migrants" and proud to lead a city as diverse as London.
However, “the numbers coming in puts massive pressure on housing and other provisions such as social services and education. What we need is managed immigration,” he added.
Meanwhile, Cameron visited Northern Ireland on Saturday as part of a tour to persuade voters to say “yes” to remaining in the EU, also known as the world's largest trading block.
“More than 60 percent of Northern Ireland’s exports go to the EU and around 40 percent of its investment comes from the EU,” he said in a statement ahead of the trip.
Johnson is expected to visit Northern Ireland on Monday.
Opinion polls have differed about the likely outcome of the referendum.
The latest poll, published on Friday by ORB for the Independent newspaper, showed support for the "out" campaign had risen to 52 percent from 48 percent from a month ago, while support to stay in the EU had fallen to 48 percent from 52 percent.