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Commons Speaker John Bercow insists his impartiality has not been affected after he revealed he had voted Remain in the EU referendum.

The Sunday Telegraph reported that he had spoken about his voting stance to students at Reading University.

A spokeswoman for the Speaker, expected to be politically neutral, said his vote against Brexit did not affect his ability to handle MPs' debates fairly.

Labour deputy leader Tom Watson called Mr Bercow "one of the great Speakers".

Mr Bercow, who was a Conservative MP before becoming Speaker, is already facing calls for him to be replaced for voicing his opposition to US President Donald Trump addressing Parliament on his UK state visit.

Talking to Reading students on 3 February, Mr Bercow said: "Personally, I voted to remain. I thought it was better to stay in the European Union than not."

He said this was "partly for economic reasons - being part of a big trade bloc - and partly because I think we're in a world of power blocs.

"I think for all the weaknesses and deficiencies of the European Union, it's better to be part of that big power bloc in the world than thinking you can act as effectively on your own."

He also said immigration was a good thing and expressed concern Labour had not done more to strike a "very clear, resonant Remain note".

Analysis: By Susana Mendonca, BBC political correspondent

Image copyright PA

As Speaker you're supposed to hang up your political colours at the door.

It doesn't stop you from having a vote in an election, but what you can say publicly becomes subject to scrutiny.

The parliamentary website states that the "Speaker must resign from their political party and remain separate from political issues, even in retirement". John Bercow's former party - the Conservatives - was divided on the EU referendum and so whichever way he voted would not have been party political.

The website doesn't specify, though, whether staying "separate from political issues" means a Speaker is never allowed to express a personal view at all.

Mr Bercow's critics are effectively saying that the Speaker shouldn't state opinions in public on politics in its entirety.

His supporters say Mr Bercow only said he voted Remain long after the actual EU referendum and that he gives every MP a fair go in debates regardless of their political views.

Mr Bercow's spokeswoman said he had voted in last June's referendum "along with millions of others".

"The record shows that he has rigorously facilitated the raising of concerns of those on both sides of this argument, as he does on every other issue," she said.

"The Speaker's impartiality is required on matters of debate before the House, and he has been scrupulous in ensuring that both sides of the argument are always heard."

But Conservative MP James Duddridge, who has tabled a motion of no confidence in him, told BBC Radio 5 live's Pienaar's Politics he was "no longer impartial" and had to go.

"There's absolutely no way Speaker Bercow can sit in the chair on European issues."

But Leader of the House of Commons David Lidington told BBC One's Andrew Marr Show that when he had served as Europe minister, Mr Bercow had not been "shy of calling" those "hostile" to the UK's membership of the EU to speak in the Commons.

His future was a "matter for members of the House" as a whole, Mr Lidington continued, and it was "really important... that the government doesn't get involved" in saying who should be Speaker.

He said the Speaker "has his very strong supporters and his critics in the House of Commons", but had to have "the confidence of the Commons as a whole".

'Honest and honourable'

On the same programme, Mr Watson said Mr Bercow "absolutely" had the backing of MPs, adding: "He's one of the great Speakers the House of Commons has seen. He gives backbenchers their voice."

On ITV's Peston on Sunday, former Culture Secretary John Whittingdale, a prominent Brexit campaigner, said he was "a bit surprised" Mr Bercow had voted to stay in the EU, adding: "We had been told privately that he was sympathetic to our cause."

Mr Bercow, who became Speaker in 2009, was "coming to the end of his time, in any case", he added.

Earlier this week, Mr Bercow defended his opposition to Mr Trump addressing Parliament.

His comments, including accusing the US president of "racism and sexism", had been made "honestly and honourably" and were within his remit, he told MPs.

Several Conservatives have criticised those remarks, though, with one saying his career could be in "jeopardy" and another that he had damaged the national interest.

Downing Street called his comments "a matter for Parliament".