Families travelling to France should set off “earlier” than normal when new exit checks at ports and Eurotunnel come into force next month.

It was “advisable” for travellers to build in extra time on days when ports are particularly busy, according to immigration and security minister James Brokenshire.

The concerns relate to new exit border checks that come into effect on April 8 – the Wednesday after Easter Sunday – and could impact families heading abroad for spring holidays.

Every tourist leaving the UK will have their passports checked at ferry ports for the first time in 20 years.

The checks will double the amount of time for a car with a family of four, prompting concerns that queues will build up, blocking major roads.

The problems are likely to be particularly acute at Dover which handles 60% of UK ferry traffic to the Continent, with 50 sailings a day.

Ferry companies have told the Home Office that family vehicles will be have to join queues of lorries on the A20 and M20, raising concerns about the safety of families in the cars, the Telegraph reported.

Trials found “significant queues (of 650+ cars) will form on days when overall car numbers exceed 7,500,” according to a letter from the UK Chamber of Shipping to MPs on the Home Affairs Committee.

Brokenshire played down concerns, saying he did not recognise the “extreme” stories about how the changes could impact travellers and insisted there were contingency plans ready.

He said the government had been working with ferry companies and Eurotunnel for the last 18 months and stressed that the checks were little different to those already carried out by airlines.

He was confident an “effective process” would be put in place and said there are “contingencies” in place for if problems do occur.

Asked on BBC Radio Four’s Today programme if he advised people to leave earlier than normal for their holidays, Brokenshire said: “Well, obviously we want people to set out in good time.”

Pushed again on whether families should “set out earlier” than normal, he added: “On busy days, I think it’s advisable for anyone to set out earlier to ensure that they‘re at their port of departure on time.”

The suggestion that families should build in extra contingency time for ferry trips over Easter will do little to allay fears that the changes could cause major delays at the border.

P&O Ferries told The Express: “The approaches to the port of Dover can get extremely busy at peak holiday times and we are concerned that the queues are going to get worse.

“We have been asked to do these checks by the government but we are expected to supply the equipment.

“We are doing this voluntarily but we have been told that if we don’t do it, it will be imposed on us anyway.”

A Eurotunnel spokesman said it can deal with up to 12,000 cars on peak days.

He said: “The smallest delay in the journey at any point in the terminal results in an immediate tailback.

“Those tailbacks – cars or trucks – are the kind of thing that can very quickly overflow on to the motorway.”

The Home Office said: “From April, exit checks will allow us to confirm a person’s departure from the UK, delivering on the coal­ition Government’s commitment to introduce exit checks.”