John Bercow, the Speaker of the House of Commons, has been criticised for suggesting that eastern European immigrants have more "aptitude and commitment" to work than British people.

Bercow made the comments during an official visit last week to the Romanian parliament, where he was asked about the debate in the UK over the lifting of European immigration restrictions on Romanians and Bulgarians at the start of next year.

While stressing that he believes controls on migration are needed, he also said that immigration had great advantages for the UK and that critics of recent immigration trends had made their case in a "bellicose and strident tone".

"I believe things should be controlled and monitored when it comes to migration – any state that wants to protect its own people should do this – but there are also great advantages," said Bercow.

"I want to underline the fact that there has been an important wave of immigrants that came to Great Britain from new member states and in many cases they came with aptitudes and a commitment, an involvement we haven't always seen in our labour force."

The UK Independence party leader, Nigel Farage, suggested that Bercow's comments breached the traditional impartiality expected from the Speaker on matters of political controversy.

Farage – who challenged the Speaker in the 2010 general election – told the Daily Telegraph: "It is outrageous that Mr Bercow is happy to overthrow the wisdom of ages and think it acceptable to comment on matters that are both highly political and deeply contentious. He is a disgrace to the office of Speaker.

"There are very good practical and constitutional reasons why the Speaker is neutral, reasons that he obviously believes are beneath his own august self-image."

But a spokesman for Bercow said his comments came in response to questions following his speech, and that he had been trying to be helpful to his Romanian hosts by rehearsing the arguments on both sides of the debate.

"He understands more than anybody the importance of impartiality in this role," said the spokesman.

"It is not something that he would go to the Romanian parliament to give a lecture on. It is just one of a series of questions he was asked.

"He was in front of the Romanian parliament answering questions about all sorts of things and just wanted to be helpful to his hosts."

Bercow's visit was organised by the Foreign and Commonwealth Office.