Home Secretary Jacqui Smith was branded "shifty, evasive and incompetent" by the Tories yesterday over the employment of illegal migrants in the security industry.
Shadow immigration minister Damian Green levelled the accusation as MPs held their first ever topical debate on immigration.
Mr Green also accused Immigration Minister Liam Byrne (Lab Birmingham Hodge Hill) of refusing to devote even a second of his speech to the "cover-up".
He said Ms Smith (Lab Redditch) had told the Commons on Tuesday that she was waiting until she had the full facts about the employment of thousands of illegal migrants before making them public.
Yet a Home Office memo dated August 30 suggested the use of "reactive lines should this issue ever come to light".
Accusing Ms Smith of trying to "cover-up a scandal" in her department, Mr Green said: "It's perfectly clear that she wished to evade any kind of public responsibility and public debate about a use of illegal immigrant workers in areas of the utmost national sensitivity."
Junior Home Office minister Meg Hillier, replying to the debate, hit back at the Tories after their attack on Ms Smith.
She told MPs: "I feel rather let down by the Members opposite and, while I've great respect for Mr Green personally, I think he's resolutely refused to answer questions about his party's cap proposal".
Meanwhile, Mr Byrne refused to estimate the number of immigrants that are set to enter the UK from Romania and Bulgaria following their entry into the EU.
He was challenged by a senior Labour MP and the Tories to give a figure but declined, although he said a points system for migration control would ensure that "only those that this country needs will be able to come".
Mr Byrne said he had learned not to make "projections" about future numbers. "Where it is possible" the Government would impose restrictions on immigrants.
Later Mr Byrne challenged Mrs Green over comments by Nigel Hastilow, who resigned as a parliamentary candidate for Halesowen, after claiming Enoch Powell "was right" on immigration.
He said: "I hope that you will join me not only in applauding his resignation but will you join me in condemning his remarks, in rejecting the arguments of Enoch Powell, in sending a clear message to this House and beyond that the days of the politics of division are over."