A senior Labour MP has urged the Home Office to properly record when migrants leave the UK after their visa expires.
Former minister Clive Betts raised concerns that Britain does not record all people leaving the country through border checks.
Instead there is a system that relies on matching passenger data with visa records.
But Mr Betts, the MP for Sheffield South East, has warned that without proper exits checks there is an increased risk of people staying and working in the country illegally.
He suggested that the system will "continue to fail" if changes are not made.
Director for visa status, Marc Owen, told the Government's Public Accounts Committee that they "were not tracking every single individual "from abroad working in the UK.
He added that his team can only know if someone has left Britain by matching airline passenger data with visa records.
Instead the Home Office relies on employers to carry out visa checks and enforcement officers to detain people for working illegally or overstaying their visas.
Between July 5 and October 31 last year there were 3,188 enforcement visits — a sharp jump from the 2,371 raids during the same period in 2023.
Arrests also rose, from 1,836 to 2,299. Between the same period, fines totalling nearly £1.9 million were handed out by the Home Office to almost 50 London businesses.
Mr Owen said: "We use our immigration enforcement services to visit illegal working places on the basis of intelligence and to collect people and to return them as they can."
Mr Betts later told the BBC that the lack of checks when people leave the country were down to the "general failure of the border system over several governments".
He urged the Government to strengthen the system and make visa checks a cornerstone of its new immigration plan.
Sir Keir Starmer's immigration "reset" proposals are expected to be laid out next week.
Strict new measures under consideration are said to include raising the English language standards required for people from abroad applying for a UK work visa.
Reports suggest that migrants will also be required to wait as long as a decade - double the current five years - before they can apply for indefinite leave to remain in Britain.
Visa applications from nationalities considered most likely to overstay and claim asylum in Britain could also be restricted under the new plans.
The Immigration White Paper is designed to bring down levels of net migration - the number of people coming to the UK verses the number leaving -which last year stood at some 728,000 people.
A Home Office spokesman said: "Under our plan for change, our upcoming Immigration White Paper will set out a comprehensive plan to restore order to our broken immigration system."
