LONDON (Reuters) – Britain will propose on Monday signing a new security treaty with the European Union after Brexit to maintain and intensify cooperation to thwart “ever-growing and increasingly cross-border threats”.

In its sixth policy paper setting out its vision for ties with the EU after it quits the bloc in March 2019, the government will say the new treaty “would be underpinned by our shared principles and should make sure our partnership has the agility to respond to the ever-changing threats we face”.

The proposal comes just days after a blast on a packed commuter underground train injured 30 people in west London, the fifth major attack this year.

“We already have a deep level of collaboration with the EU on security matters and it is in both our interests to find ways to maintain it,” Brexit minister David Davis said in a statement.

“A new security treaty with the EU would be underpinned by our shared principles, and should make sure our partnership has the agility to respond to the ever-changing threats we face.”

Britain has published a series of “future partnership” policy papers to try to nudge talks with the EU forward, after they have stalled over the divorce settlement, especially over the so called Brexit bill.

Security cooperation is seen by government officials as one of their strongest arguments to gain leverage in the complicated talks to unravel more than 40 years of union.

Amber Rudd, the interior minister, said Britain was one of the leading EU contributors to a range of measures, such as data and evidence sharing, extradition measures and to the EU’s policy agency Europol.

“Recent events in the UK and across Europe have shown the criminal and terrorist threats we face are varied and increasingly international. The long-standing collaboration we have with our European partners allows us to jointly address these threats and keep our citizens safe,” she said.

“As we prepare to leave the EU it is therefore vital that we agree a new way to ensure continued security, law enforcement and criminal justice cooperation.”