More than two million immigrants will arrive in Britain every 10 years unless strict new controls are introduced, according to a new campaign group.

Migration Watch UK says there are no economic benefits from large-scale immigration and is calling for "greater urgency and resolution" from the government to prevent it.

The campaign group warns that failing to address the situation "will play into the hands of the far right who seek to exploit the situation for their own ends".

On present patterns, two-thirds will settle in London and the South East

Sir Andrew Green

Its warnings were described as "scaremongering" by Keith Best, chief executive of the Immigration Advisory Service.

The Joint Council for the Welfare of Immigrants (JCWI) said Migration Watch UK's findings ignored the valuable role overseas workers play in the UK economy.

The debate came ahead of a meeting between Home Office officials, the Immigration Advisory service and Refugee Legal Centre about plans to fast track the appeal system for asylum seekers.

More than 180,000 people migrated to Britain in 2000 according to official figures, Migration Watch said.

The group claimed a further 60,000 people overstay their visas or enter the country undetected each year - bringing the total to 240,000.

What this does is give the far right ammunition to propagate their own particular views

Joint Council for the Welfare of Immigrants

Former diplomat Sir Andrew Green, who established the group with Oxford University academic Dr David Coleman, said: "Even using very cautious estimates for illegal immigration, we are approaching a quarter of a million migrants a year for the first time in our history.

"That means a population the size of the city of Cambridge being added every six months or a population the size of Birmingham every five years.

"On present patterns, two-thirds will settle in London and the South East."

'Debate'

The immigrants would "have a profound effect on the nature and shape of our society for decades to come", Sir Andrew predicted.

He told BBC Radio 4's Today programme: "We believe that there should be a rational debate on the facts and we just don't believe that the present situation is either sustainable or in the interest of any group in our society."

Derek Betts, case work director for JCWI, rejected Migrant Watch UK's findings, and said: "What this does is give the far right ammunition to propagate their own particular views".

Mr Betts said immigrants have been essential to Britain's economy for years and the country was dependent on new arrivals to fill many types of job.

'Robust'

Speaking to BBC Radio 4's Today programme Keith Best was critical of Migration Watch UK.

He said: "I think they are being somewhat naive if they think that putting out some of the figures they have is not going to be picked up on by the tabloid press and hyped up in order to try to scare the British people witless."

Rosie Winterton, Parliamentary secretary in the Lord Chancellor's Office, said the UK needed a system which "is fair, but is also robust".

She said the government hoped to shorten the time taken to consider immigration appeals.

It was important that people had a speedy decision, whether or not they were to return to their original countries, she added.

A Home Office spokesman said: "We take the issue of illegal immigration very seriously.

"And there are a number of things we are doing to combat it at a European and domestic level."