There are concerns over the further influx of foreign workers

Party immigration spokesman Damian Green said ministers had to learn from the "unprecedented numbers" who arrived in the UK after the last EU expansion.

He called on the government to use existing EU powers to control immigration to "reduce tensions" and boost the economy.

Trade Secretary Alistair Darling said migration would be "properly managed."

He said no date had yet been set for Bulgaria and Romania's accession but that when it was there would be no "open door" policy.

"What we need to do is balance the skills that we require - and yes, our economy does require skills in various areas - and at the same time having a system that is properly managed so we can take care of all the other things we need to consider, like the healthcare system, the education system and so on."

There is a very sensible, moderate, practical case to make that we cannot simply have uncontrolled immigration from these new countries. Damien Green Conservative immigration spokesman EU candidate countries See interview

BBC political correspondent Laura Kuenssberg said immigration was once a key Conservative policy but, having lost three elections, the party had moved away from emphasising it.

But debate on the issue was increasing, with former Labour minister Frank Field and senior backbencher John Denham voicing their opinions recently so it was not surprising the Conservatives had joined in, she said.

It comes as a poll for the Sunday Times found 77% of people wanted the government to set a strict limit on the number of immigrants allowed into Britain each year.

The UK government has yet to indicate whether workers from Romania and Bulgaria will enjoy the full working rights associated with being an EU citizen from the outset.

While other EU countries imposed quotas on migrant workers after the last accession, the British government's estimates that as few as 13,000 would arrive in the UK have been far exceeded.

Migrant workers should only be allowed in if it can be proved there is an existing skill shortage Bob Cotton British Hospitality Association Send us your comments

Mr Green, speaking on BBC News 24 Sunday, said 600,000 had arrived.

"What we are saying is that we should learn from the government's mistaken planning over Poland and the other countries and we should use the powers that are there in the [EU] treaty to regulate the flow, to control the flow of people coming from Bulgaria and Romania."

Another influx could "put unacceptable pressure on public services, on school places, on the provision of housing, which causes big problems for certain local communities".

He said a leaked Home Office report had suggested 45,000 criminals could be considering entering the UK.

"That's one concern but even without the criminal element, there is a very sensible, moderate, practical case to make that we cannot simply have uncontrolled immigration from these new countries."

He did not put a figure on how many Bulgarians and Romanians should be allowed in, saying it depended on what controls other European countries imposed.

"What's really important about immigration is to strike the proper balance so we can maintain community cohesion in this country, we can reduce tensions and we can benefit our economy."

Business leaders have also urged the government to take action.

Susan Anderson of the Confederation of British Industry said: "There is a strong argument to pause for a period before opening up to workers from further new member states while we learn the lessons from experience to date.

We could attract more than 10,000 Romanians at all levels for the construction industry as well as the hotel and catering service industries in the UK Dominic Ryan Premier Global Recruitment

"Present systems for monitoring and controlling migration need to be improved."

Bob Cotton, chief executive of the British Hospitality Association, agreed "there should be a pause".

"Migrant workers should only be allowed in if it can be proved there is an existing skill shortage - such as for chefs - and that job applicants have acceptable, proven qualifications."

Dominic Ryan, managing director of Bucharest-based Premier Global Recruitment, said he had 7,000 people on his database eager to work overseas including in the UK.

"Virtually everybody in Romania is highly educated and the vast majority of those who apply to us are skilled and semi-skilled - they are an exceptionally qualified workforce," he said.

"Our research shows we could attract more than 10,000 Romanians at all levels for the construction industry as well as the hotel and catering service industries in the UK, if we had contracts to do so."