Hundreds of migrants hoping to enter the UK are camped near Calais
An amnesty for illegal immigrants would be a "well intended road to hell", says immigration minister Phil Woolas.
He was asked about London mayor Boris Johnson's suggestion that long term illegal immigrants should be able to "earn" the right to stay.
But Mr Woolas told MPs on the home affairs committee it would increase the "pull factor" for illegal immigrants.
He also said he did not recognise figures suggesting there were 750,000 illegal immigrants in the UK.
Mr Woolas was being questioned about the new points-based immigration system for people from outside the EU.
He said the official position was that the government did not know how many illegal immigrants were in the country and added: "We haven't done a detailed study on this for three years now, four years - so I don't know."
Mr Johnson has said that deporting thousands of illegal immigrants was "just not going to happen" and that an amnesty for those meeting certain criteria would be "morally right" as they could contribute in taxes towards the rest of society.
But Mr Woolas said: "What I do believe is that if one were to do what the mayor suggested it would make the problem worse not better because the pull factor would increase and the people traffickers would make more money."
"I think an amnesty is a well-intended road to hell," he said.
He was appearing before the committee after a GMTV interview in which he said refugees attempting to enter Britain via Calais were "locked out, not queuing to get in".
Not asylum seekers
Conservative committee member David Davies asked why, if security was so good, people were still "marching through dozens, sometimes, of European Union countries" to get to Calais with the aim of getting to the UK.
"It is because they know the benefit system is far more generous in the United Kingdom," he said.
"Why don't they claim benefits in France?" he said.
Mr Woolas said he did not accept that but said most people in Calais were not seeking asylum, if they were they would seek it in France.
He said similar questions were asked in France about why people from Algeria headed to Marseilles rather than Spain - or in southern Spain about people from western Africa who did not head to Italy.
But he said he accepted that "the message the people traffickers are sending out to people in the country of origin is exactly that there is a promised land in the United Kingdom and our efforts are there to make sure that while we protect genuine refugees ... we need to put the record straight as to what our immigration management policy is, and that it is improving."
Mr Woolas told the committee he had had a meeting with his French counterpart, and said people found in camps at Calais were being returned to Iraq and Afghanistan.
"Our intention is to announce a package of measures to move the situation on," he said.
"Essentially we are in a battle with people traffickers - it's the people traffickers who are raising the expectations of these people and it's up to us with our French colleagues to put the facts right to them."
Later he said Britain was trying to reach agreement with the French on plans for a new detention centre in Calais.
Illegal immigrants could be held in the centre after passing through British immigration controls in France - then sent back to their home countries on charter flights.
Mr Woolas said the costs and construction timetable were still being discussed. It is hoped a deal will be reached by the end of April.
"We are not looking at a parallel situation to Sangatte. These people are locked out of the UK," he said.
But Conservative immigration spokesman Damian Green said: "This new detention centre will be a waste of money if it only deals with those who have passed through immigration controls.
"The real problem is the increasing numbers who are gathering at the coast with no intention of coming here legally."
In 2002, Sangatte refugee camp near Calais was closed in an attempt to stem the flow of illegal immigrants crossing the Channel into the UK.
Official figures show the number of illegal immigrants detected entering Kent from Calais fell 88% from more than 10,000 in 2002 to 1,500 in 2006.
But charities and officials in Calais want to create a welfare centre for some 500 asylum seekers who are sleeping rough in the port town.
France's Immigration Minister Eric Besson has previously said that another Sangatte was "out of the question".