"John Bercow is meant to be an impartial Speaker of the Commons, not a mouthpiece for EU propaganda. Now he’s exposed his pro-EU views, he is hardly likely to give eurosceptics a fair hearing in parliamentary debates," said Tim Aker of the Get Britain Out campaign group.
"Bercow is there to defend Parliament; he should be supporting parliamentary sovereignty, not the EU’s constant power grabs," Britain's Daily Express cited him as saying.
Bercow's statement came in a discussion with students at Vilnius University during a visit to Lithuania earlier this week.
"The idea that we will march through the exit door is extremely unlikely,“ he said during a discussion with students of Vilnius University's International Relations and Political Science Institute.
"We will remain in; there will be disagreements but we will be part of the EU," he said.
In Bercow's words, a majority of voters in the UK will choose to stay in the EU if that referendum is held, regardless of euroskeptical views.
In an interview to BNS after the meeting, he said he personally supported UK's further EU membership.
In January, British Conservative Prime Minister David Cameron said his party would run for the next parliament in 2015 with the promise to renegotiate London's EU membership. The prime minister also said an "in or out" referendum would be held by 2017 following membership renegotiation, if he was reelected.
Given an in-out referendum on EU membership tomorrow, 50 percent would vote “out” against 33 percent “in” and 17 percent who would not vote either way, according to a poll by Harris Interactive for the Financial Times.
Nevertheless, Bercow believes people would not vote for the withdrawal.
"They may grumble, they may criticize, they may argue for change, but will they want to go marching through exit door? I do not believe they will," he said.