The Prime Minister had paid tribute to the millions of Jews and other targeted groups killed by the Nazi regime minutes before making his controversial aside while attacking Labour.
Yvette Cooper, the former shadow Foreign Secretary, later raised a point of order to call on Mr Cameron to withdraw his comment.
“In the light and spirit (of Holocaust Memorial Day) doesn’t the Speaker think it was inappropriate for the Prime Minister to use language referring to the refugee crisis in Europe to talk about a ‘bunch of migrants’?” she asked.
Ms Cooper requested that the House of Commons demand the comments be withdrawn but the Speaker, John Bercow, declined and said it was up to Mr Cameron to comment if he chose to.
On Twitter, shadow Home Secretary Andy Burnham said the moment showed the Conservative leader’s “mask slipping”.
“He just dismissed desperate people fleeing conflict as a “bunch of migrants” – on Holocaust Memorial Day,” he added.
Scores of critics were noting the timing of the comment, which sparked a storm of criticism as people highlighted the persecution faced by many of the refugees fleeing to Europe.
Determined to get his point across, one MP really took PM Cameron’s comment and ran with it … exposing the latent racism which has plagued Britain.