Police and crime commissioners are warning of the risk to public safety from a no deal Brexit.
Conservative, Labour and independent representatives said they have discussed the issue with the National Crime Agency and National Police Chiefs’ Council and fear what could happen without agreement between the UK and EU.
They have written to Home Secretary Sajid Javid to confirm the Home Office has developed a contingency plan for a no deal Brexit.
The letter was discussed at a national PCC meeting in mid-July and sent last week. It is signed by Tory Matthew Scott, Labour’s Lord Willy Bach, and independent Martin Underhill.
It says: “We understand that considerable additional resource would be required for policing to operate using non-EU tools and that such tools would be sub-optimal - potentially putting operational efficiency and public safety at risk."
It continues: "There are 32 Law Enforcement and National Security Measures [Lens] that are used on a daily basis in an operational policing context.
"Unless the government is able to negotiate the retention of these measures following the UK's withdrawal from the EU, police and law enforcement agencies face a significant loss of operational capacity.
"As police and crime commissioners, we are increasingly concerned that such a loss of capacity could pose significant risks to our local communities."
They add that Brexit negotiations come at a time when the threat from foreign national offenders targeting the UK from abroad is increasing.
They also say that with the implementation period unlikely to be known until October this year, the five-month window until the end of March 2019 is "likely to be very challenging".
They have asked for a meeting with the Home Secretary to discuss "preparations, contingencies and the financial implications of post-Brexit policing".
In 2016 Sir Hugh Orde revealed on Police Oracle that chiefs had analysed the impact of leaving the EU in 2013 and identified 13 elements “without which we would struggle to protect citizens in this country”.
A Home Office spokesman said: "There is widespread recognition that the UK and EU can most effectively combat security threats when we work together. It is important we maintain operational capabilities after Brexit - and we will continue to make this case to the European Commission.
"We are confident that an ambitious agreement on future security cooperation can be reached — but it is the duty of any responsible government to prepare for every eventuality, including no deal.
"With that in mind, we are working closely with operational partners on contingency planning so we can ensure the safety and security of our citizens in all scenarios.”