Britain could hand over its continental border controls to the French under radical plans to meet Government spending cuts to be finalised tomorrow.
The proposals would end the dual immigration system at the ports of Calais, Bologne, Dunkirk and the Channel Tunnel at Coquelles, where UK officers operate security and immigration checks.
It would leave French immigration in sole control of cross-Channel security, The Independent has learnt. A similar proposal has been outlined for Eurostar immigration controls in Paris. The highly controversial move would reverse the cross-Channel controls introduced under the Labour Government in 2004.
Last night British immigration staff denounced the proposals, claiming that the policy would amount to "handing over the control of UK borders to another country". Paul O'Connor, the Home Office group secretary of the Public and Commercial Services union (PCS), warned that the cuts would lead to more illegal immigration.
Under alternative measures, which would leave the "juxtaposed controls" in place, staff would be offered relocation packages so that UK Border Agency (UKBA) immigration officers could move across the Channel.
Both the proposals would save millions of pounds from the £2.4bn UKBA budget by reducing allowances and travel costs between the UK and France. Under the present scheme, immigration staff are paid for travelling to and from the checkpoints.
The UKBA has earmarked 7,000 job cuts over the next four years, ahead of the Comprehensive Spending Review, which will see its budget slashed by between 25 per cent and 40 per cent.
Unions fear that this will lead to more use of private security companies, such as G4S, to take up the slack at a lower cost. But Mr O'Connor said that this would go against the previous Government's promise not to "part-privatise" the UKBA.
"That promise was given by ministers on the floor of the House," said Mr O'Connor. "In terms of frontline security, our members are the first port of call to maintain proper border controls. If they decide to cut one in three this country will be less safe."
Lin Homer, chief executive of the UKBA, said: "Our priority is always to keep the border secure and to control migration."
She added: "The new Government is focused on reducing the public deficit and the UK Border Agency will take its share of cuts to public service budgets. We will not know our final budget until the Spending Review is announced.
"Through modernisation and new technologies, the UK Border Agency was already working to reduce its budget and ensure value for money for the taxpayer. We will build on the progress that we have made. Where we need to make further reductions, we will focus on cutting overheads, layers of management and support services to protect frontline services."
In an agreement between the Government and the then French Interior Minister, Nicolas Sarkozy, all UK-bound passengers travelling from Calais and Dunkirk are subject to checks by UK immigration officers before they travel. Passengers are refused permission to set off for the UK if they do not have the proper paperwork.
The move, which was designed to make it more difficult for illegal immigrants to reach Britain, was part of a package of measures that included the closure of the Sangatte detention centre.
In 2008, UKBA officers searched more than a million vehicles and stopped 28,000 attempts to enter the country illegally. From January until the end of July 2009, technology used in checks at ports helped in the seizure of illegal drugs worth more than £143m, and British officers seized in excess of 340 million cigarettes, representing a potential loss of £65m in tax revenue.
The agreement on immigration controls is a reciprocal one, and French border police are stationed at Dover to check passengers travelling to France, extending the controls they already operate at the Eurostar stations of Waterloo and Ashford, and at the Eurotunnel Terminal at Cheriton.