Plans for more co-operation between EU states on immigration and fighting crime will not mean key UK powers are lost, the government is insisting.
The proposals could lead to a force of EU border guards
The plans are being put to a full Commons debate after an MPs' committee said they raised several concerns.
The Conservatives say the proposals would end the British veto on asylum and immigration measures.
But as the debate began, Home Office Minister Caroline Flint accused the Tories of spreading "myths".
European ministers agreed a five-year co-operation plan on criminal justice, visas, asylum, immigration, police and customs cooperation in 1999.
That programme is now coming to an end and MPs are being asked to endorse the European Commission's plans for the next five years.
The Commons European scrutiny committee says approval should be withheld until the practical benefits seen over the last five years and those expected under the new plan are assessed.
Its report said: "It bodes ill for the future if, on such sensitive matters, the commission envisages reliance on qualified majority voting to impose on member states legislation to which they are opposed."
Tory shadow home secretary David Davis said the plans would see the British veto being given up on asylum, immigration, visas and immigration, which would now be decided through weighted votes between countries.
"That is not cooperation, that is decisions effectively driven by Brussels," Mr Davis told BBC Radio 4's Today programme.
The issues caused great political argument in Britain and it was incredibly important they could be decided in Parliament, he argued.
Mr Davis argued plans for a European public prosecutor, border guards and giving Europol investigative powers would give the EU "the trappings of a nation state".
The government says it supports the creation of a European border agency but does not want a corps of border guards.
It says it will only agree to a European public prosecutor if it is in Britain's interests.
Home Office Minister Caroline Flint denied there would be "harmonisation" of measures on asylum and immigration.
She said Britain was able to "opt in" where it wanted more co-operation.
Opening the debate, Ms Flint denied the plans threatened British sovereignty.
"We will ensure, along with other member
states, that the EU continues to respect the distinct and diverse legal
traditions of member states," she said.
"In particular the prosecution of individuals must remain a national
competence and we do not support proposals such as a European public
"But what we have also to ensure is that we have safeguards to make sure that
if there is any threat to our legal system in this country and our way of
carrying out procedures in criminal law we have an emergency brake we can step
on to make sure there would have to be a unanimous decision on this issue."
Earlier, outgoing European Commissioner Chris Patten has argued that European integration was at the "end of the road" with Britain's case winning through.
The ex-Tory chairman told the Times newspaper on Thursday: "Everyone else thinks it is going in our direction.
"Everyone else thinks that the constitutional treaty, for example, represented a huge achievement for British diplomacy. Everyone believes it except us."