By Jim Reed
Newsbeat crime reporter
The UK Border Authority has told Newsbeat it deported a record 66,000 illegal immigrants last year as part of a new attempt to cut the number of people working in Britain without permission.
It's thought that 750,000 illegal immigrants live in the UK
Immigration officers arrested 10,000 people in raids and sent 5,400 foreign criminals back to their home country, up from 4,200 in 2007, according to the Home Office.
But critics say the number of arrests is still "a drop in the ocean" compared to the 750,000 immigrants it is now thought are living in the country without official permission.
They say it would be cheaper and fairer to give illegal workers the full right to a job if they can prove they have been here for six years and can provide employer and character references.
Newsbeat went along with five Border Agency officers as they carried out snap inspections of firms in Southampton suspected of employing illegal workers.
Chief Immigration Officer Simone Sheppard said her team are sent on three or four raids a week.
"It's only over the last seven years that we've started arresting people without the police," she said.
"We are now looking more at fining the companies employing illegal workers. It's got a lot more busy, I must say."
Chief Immigration Officer Simon Sheppard says she's been busier
On the first raid at a a curry house in the city centre, the officers interviewed 15 kitchen staff and found a single Bangladeshi man suspected of overstaying his short-term marriage visa.
"On the face of it, it might not look like he's doing anything wrong," said Simone. "But we've got to look at the bigger picture.
"Sometimes these workers been smuggled into the UK. They don't know why they are coming, their passports are taken away and they might have to work seven days a week for a pittance of a wage.
"We've got to help these people and stop this smuggling."
A report by researchers at the London School of Economics for the city's mayor Boris Johnson claims that one person in every 84 living in Britain is now in the country illegally.
Most will have overstayed their visas after arriving as students or on temporary work contracts although some will have been smuggled in by organised gangs.
Thousands of people met in Trafalgar Square over the bank holiday weekend in support of an "earned amnesty" for immigrants that have lived here illegally for six years.
The pressure group Strangers Into Citizens, which organised the rally, says the government strategy of heavy fines and document checks is "inhumane, costly and complicated".
The group's director of policy Austen Ivereigh told Newsbeat: "They had an amnesty in 2005 in Spain and made about 600,000 people legal. It resulted in fewer people coming in, so it's actually a good way of tightening the borders.
"They start to pay taxes whereas before they didn't," he said. "And legal workers are not undercut by migrants being paid half the minimum wage."
But critics of the idea claim it could encourage more immigrants to try to cross the border, put extra pressure on services like hospitals and schools and cost UK taxpayers billions of pounds.