Holidaymakers could face queues at Eurotunnel and ferry ports when passport checks on passengers leaving Britain are introduced in early April, MPs have warned.
The Commons’ home affairs select committee heard that the start date for the checks has been pushed back by one week to avoid introducing the new system over the busy Easter weekend.
Sir Charles Montgomery, the director general of the Border Force, also told MPs immigration officers have detained 6,000 illegal immigrants in Britain from April to December last year.
Sir Charles confirmed the technology being used to carry out exit checks has yet to be finalised with just eight weeks to go.
He also told MPs that coach parties of children aged under 16 will be excluded from the checks, in a bid to ensure delays are cut to a minimum.
Ministers had said the exit checks would come in by the end of March but after listening to concerns from port operators they will now begin on April 8, two days after Easter Monday, Sir Charles said.
The checks will involve operators recording passport information on all travellers and passing the details on to the Home Office, which will use the details to identify immigration offenders.
Yasmin Qureshi, a Labour MP who sits on the committee, said: “We have heard from Eurotunnel and ferry companies that there are logistical problemsin carrying out exit checks on people in coaches.
“It’s going to cause inevitably a lot of delays. What is going to be done?”
Sir Charles replied: “The coach sector is the most difficult of all logistically and that has been the focus of trials and testing.
“We still have to refine the process to ensure it works as smoothly as possible.
“I’m confident we will have a solution come the live date.”
The director general said immigration officers have detained more than 6,000 illegal immigrants who managed to make it to British soil so far this financial year, up to the end of December, equal to more than 20 a day.
He said the figure was potentially “flaky” because some other types of immigrants – such as foreigners who have overstayed their visa – may falsely claim to have come here clandestinely when they are detained.
“The best that I can offer is that this year there has been about 6,000 detections in-country,” he said.
Sir Charles also said more than 30,000 illegal immigrants were stopped in France by British immigration officers working at Calais and other terminals between March last year and the end of January – or 90 a day.
He added that he would never be able to guarantee the authorities would be able to stop all immigrants seeking to enter this country illegally.
“I cannot look this committee in the eye and say I can operate 100 per cent control so 100 per cent of clandestines will not get across the border,” said Sir Charles.
It came as Theresa May, the Home Secretary, announced a former MI5 officer has been appointed to be the next independent chief inspector of borders and immigration.
David Bolt, who has also served in a national intelligence role for the now-disbanded Serious Organised Crime Agency, replaces John Vine, who left the job in December, seven months before his contract expired.
Mr Bolt has been appointed to the £130,000-a-year job on a fixed term two-year contract, one year shorter than his predecessor.
He is currently chief executive of the International Federation of Spirits Producers, which combats international trade in counterfeit spirits.
Mrs May also said Britain has signed up to a European database which will help keep criminals out of the country.
Ministers have negotiated access to the Second Generation Schengen Information System, known as “SIS II”, which was established in 2007 and is already used by 28 European countries.
Data on SIS II includes details of about 250,000 wanted or missing people.