MPs have warned of major border disruption on day one of Brexit, saying the government plans for an increase in border staff is completely unconvincing.
The Commons Home Affairs Committee said urgent action was needed and if it was not taken, there was a risk that Kent would be gridlocked on “day one” of Brexit.
It is the latest warning about the impact of Brexit on how the UK's borders will be secured.
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Committee chairman Yvette Cooper said: “Contingency planning is essential. If the Government gets this all wrong, we could be facing Operation Stack on steroids.”
She said: “As things stand, the Government is running the risk of celebrating their first day of Brexit with the sight of queues of lorries stretching for miles in Kent and gridlock on the roads of Northern Ireland, which would be incredibly damaging to the UK economy and completely unacceptable to the country.”
In their report, MPs say not enough extra border staff will be recruited to deal with customs checks and the government needs to speed up its contingency plans.
They warn there could be a repeat of events in 2015, when Operation Stack was in place for several weeks.
"Security must not be put at risk by government failure to plan," it says.
The report warns that rapid changes and a failure to plan could see the UK facing delays and traffic jams at ports similar to those experienced in July 2015.
That is when French ferry operators went on strike and Operation Stack was implemented to ease major problems.
It warns any change to customs arrangements after March 2019 will require similar investment and planning at the EU side of the border - especially in France, Belgium and Ireland.
Yvette Cooper MP, said: "The Government's border planning for Brexit is extremely unconvincing.
"The Government should be aiming for transition arrangements which require no change at all in customs and border requirements as everyone is running out of time to make any staffing, infrastructure or procedural changes - and they risk long delays at the border, both in the UK and abroad.”
HM Revenue and Customs (HMRC) - which handles customs checks - has said it will need an extra 5,000 staff to cope with the extra workload.