David Cameron has come under fire for referring to a "bunch of migrants" when describing Europe's refugee crisis.
Former Labour leadership hopeful Yvette Cooper asked the Prime Minister to withdraw his comments, which were made in response to Labour leader Jeremy Corbyn's visit to the makeshift Calais camp known as the Jungle.
Ms Cooper, who is chairing Labour's refugee task force, suggested the PM should use "much more statesmanship-like" language on such a "complex and sensitive" issue, particularly given ongoing commemorations of Holocaust victims.
Speaking during Prime Minister's Questions, Mr Cameron brushed off criticism of the Government's tax agreement with Google by claiming Mr Corbyn and shadow chancellor John McDonnell do not stand up to anyone.
He added they had "met a bunch of migrants in Calais and said they could all come to Britain".
Speaking outside the chamber, a senior Labour source said: "The people we saw at Calais and Dunkirk over the weekend were families, kids, babies... to consider those people we saw as a 'bunch of migrants' demonstrates an attitude that is entirely unacceptable to a humanitarian crisis on our doorstep."
Commons Speaker John Bercow ruled Mr Cameron's comments were not "disorderly" nor "unparliamentary", adding people will "make their own assessments" of the issue.
Several Labour MPs objected to the comments on Twitter, describing them as "shameful" and the PM as "odious".
Comedian David Baddiel also expressed concern, writing: "Not the right day #HolocaustMemorialDay for the bunch of migrants thing."
Raising a point of order in the Commons, Ms Cooper told Mr Bercow: "The House will have heard many tributes made to Holocaust Memorial Day today and the Holocaust Educational Trust campaign doesn't stand by.
"In that light and in that spirit, don't you think that it was inappropriate for the Prime Minister to use language referring to the refugee crisis in Europe and talk about 'a bunch of migrants'?"
Other Labour MPs could be heard saying "disgraceful" as Ms Cooper repeated the PM's comment.
Ms Cooper went on to the Speaker: "Do you think it'd be appropriate for the House to ask the Prime Minister to withdraw that language, to use much more statesmanship-like language about the need to build a cross-party consensus on such a complex and sensitive issue?"
Mr Bercow replied: "You speak with enormous experience in this House and I respect what you say.
"I completely identify and empathise with your observations about Holocaust Memorial Day, which you and I on other occasions have marked at events together - so I take what you say extremely seriously.
"I do have to say to you and the House that the observation in question was not disorderly, it was not unparliamentary.
"Everybody must take responsibility for the remarks he or she makes in this House and it is very clear that you would not have used that term.
"It is open to the Prime Minister to comment on it if he wishes but I am not entitled to try to oblige him to say anything on the matter.
"But you have made your point very clearly and it's on the record and people will make their own assessments of this matter."
Earlier, Mr Cameron had told Mr Corbyn: "All those people filling in their tax returns are going to be paying lower taxes under this Government, that is what's happening.
"And I have to say to you, you can if you want criticise HMRC but HMRC's work is investigated by the National Audit Office and when they did that they found that the settlements that they have reached with companies are fair, that is how it works.
"The shadow chancellor's pointing - the idea that those two right honourable gentlemen would stand up to anyone in this regard is laughable.
"Look at the record over the last week - they met with the unions and they gave them flying pickets.
"They met with the Argentinians, they gave them the Falkland Islands.
"They met with a bunch of migrants in Calais, they said they could all come to Britain.
"The only people they never stand up for are the British people and hard-working taxpayers."
A senior Downing Street source later said the Prime Minister had been "referring to the fact that the Labour approach of effectively opening the doors and allowing people to flow in would just provide an incentive for more people to come to Calais and wouldn't deal with the issue but would actually make the issue much worse".
Asked whether Mr Cameron thought his choice of words was acceptable, the source said: "The Prime Minister thinks that the key thing here is to get the policies right, and I think that's what the people of Britain are concerned about.
"The policy we are proceeding with is to give nearly £1.2 billion to support people who have been forced from their homes by the Syrian conflict with shelter and food, and also to take refugees from the region rather than providing an incentive for people to make that dangerous journey."
A Labour source rejected the suggestion that the party would "open the doors" to migrants, pointing out that Mr Corbyn had said priority should be given to refugees - particularly children - with links to Britain and that applications should be processed more quickly.
Labour MP Kate Green (Stretford and Urmston) told BBC2's Daily Politics: "I was shocked when I heard the Prime Minister say it. It was offensive, it was hurtful and it was divisive.
"It is not the first time we have heard David Cameron slip up in this way."
Culture Minister Ed Vaizey told the same programme: "We always talk about language, people will have their views.
"The Prime Minister was making the point that he does not agree with Jeremy Corbyn that the people camped in Calais should come to this country and be given a free pass."
Speaking later outside the chamber, Lib Dem leader Tim Farron said: " On Holocaust Memorial Day, the Prime Minister chose to refer to desperate refugees fleeing from war as a 'bunch of migrants', a statement which diminishes his office and our country.
"Whether Mr Cameron planned to use this phrase in advance or whether it was an off-the-cuff throwaway remark it shows his true attitude towards those most in need. I call on him again to offer safe haven to 3,000 young children who desperately need our help."