The UK faces being excluded from Europe’s anti-trafficking unit after Brexit, senior MPs and experts warned last night. The unit is coordinating international investigations into the deaths of 39 people whose bodies were found in the back of a lorry in Essex last week.

The warning came as on Saturday the driver of the truck, Maurice Robinson, was charged with 39 counts of manslaughter and conspiracy to traffic people over the deaths in Grays. The 25-year-old will appear at Chelmsford magistrates court tomorrow, where he will also face 39 counts of conspiracy to assist unlawful immigration and money laundering.

The anti-trafficking unit involved in the case, the European Migrant Smuggling Centre, is part of the EU’s law enforcement agency, Europol, and has been at the heart of a global inquiry into the tragedy. A Europol source said investigators at the centre were “working around the clock trying to put together the pieces of the puzzle”.

The unit is regarded as the most sophisticated organisation of its kind in Europe, with unrivalled ability to track cross-border crime and a huge database of smuggling networks.

But the UK’s ability to participate in its work after 2020, when the post-Brexit transition period with the EU is due to end, is now in serious doubt. MPs and anti-trafficking experts said it was clear from the government’s own statements that the UK would be excluded from Europol and its agencies in the event of a no-deal Brexit, and would at best have downgraded access even if a Brexit deal were done.

The chair of the Commons select committee on home affairs, the Labour MP Yvette Cooper, said that she was seriously concerned that the government had no plan as to how to ensure continued UK involvement.

Having put questions to the home secretary, Priti Patel, last week, Cooper told the Observer the tragedy was “truly awful” and that she was deeply alarmed at the apparent lack of planning to ensure full access to the EU unit and its databases even in the event of a Brexit deal. “The government’s plans mean we could lose membership of Europol, including its European Migrant Smuggling Centre, at the end of next year if a new security partnership and treaty isn’t agreed in time.

“The government itself has said this would mean a security downgrade and even in the best possible scenario there would be a substantial capability gap due to our loss of access to data and data-sharing systems and ability to lead operations as we currently do, including on human trafficking. At a time when we face a growing problem with this terrible crime it would be irresponsible to lose our close involvement with Europol and the Smuggling Centre, or to lose access to the huge criminal databases that help solve crimes.”

She added: “It is extremely concerning how little progress appears to have been made on developing post-Brexit plans for security.”

This point was also stressed by the Tory chair of the Commons intelligence and security committee, Dominic Grieve: “The dreadful tragedy highlights the need for international cooperation on people trafficking. Leaving the EU will make that much more difficult. At present there is complete uncertainty as to whether we will be able to continue working with this unit.”

Dominic Grieve said the tragedy highlighted the need for international cooperation on trafficking. Photograph: Jonathan Hordle/Rex/Shutterstock

Europol officials say that in the event of no deal, British police officers would be removed from Europol’s headquarters in the Hague. “It’s a very bleak prospect,” said a source. The source added it remained completely unclear what the organisation’s future links would be with police in the UK.

Senior figures at the United Nations also said that Brexit risked undermining the UK’s ability to tackle people smugglers and trafficking syndicates. The UN’s trafficking envoy, Maria Grazia Giammarinaro, told the Observer that withdrawing from Europol and Eurojust, which facilitates judicial cooperation among countries to tackle serious organised crime, could curtail the UK’s ability to conduct the transnational investigations required to dismantle smuggling networks. “Information sharing is crucial. Trafficking is very often a transnational crime, so the exchange of hot investigative information helps a lot. In addition, the European Union has very effective tools such as joint investigation teams that have proven very effective in sophisticated investigations,” she said.

Meanwhile David Wood, former director general of immigration enforcement at the Home Office, told the Observer that pressure on UK ports would increase dramatically after Brexit and that the risk of tragedies like last week’s would increase. He said Brexit would also involve the creation of a new visa regime that would involve a “whole new tranche of individuals” who were not eligible for entry to the UK, which demanded greater levels of enforcement. “That will be a new distraction and so things are likely to deteriorate. The resource you’ve got to deploy has already been reduced by austerity. The focus on small ports, for example, becomes extremely diluted.”

A Home Office spokesperson said intensive work was going on to ensure the UK would have continued involvement in Europol and its agencies after the end of the transition period in 2020. “The continued safety and security in the UK remains our top priority. The deal secured by the prime minister – including a close and ambitious security partnership – is the best way to protect our operational cooperation with European partners.

“We are actively engaging EU member states – in conjunction with operational partners – to prepare for all scenarios. This includes making sure that in no deal we are ready to transition law enforcement cooperation between the UK and EU member states and non-EU alternatives and we will continue to cooperate closely with Europol, including the European Migration Smuggling Centre, in any scenario.”

The Labour MP Stephen Doughty, a member of the home affairs select committee, added: “With all the focus on the economic aspects and damage to business and trade of Brexit, there has been far too little attention paid to how it will make us less safe and degrade our security cooperation in a whole range of areas. We lose access to crucial databases and information-sharing systems, which are vital.”

Police were still questioning three other individuals on Saturday in custody on suspicion of conspiracy to traffic people and manslaughter.

Elsewhere, attention shifted towards the remote Vietnamese province of Nghe An province where many of the 39 victims are believed to have begun their doomed journey. Detective chief inspector Martin Pasmore of Essex Police, leading the largest murder investigation in the force’s history, urged members of the Vietnamese community in Britain and abroad to help identify the 31 men and eight women who died after being smuggled into the UK last week.