Government’s Brexit position paper on defence strikes unexpectedly positive note as Boris Johnson praises EU’s impact.

Britain will offer to agree positions on foreign policy with Brussels and contribute to joint military operations after leaving the EU, according to the government’s Brexit position paper on defence.

The foreign secretary, Boris Johnson, said it was important to make sure the UK’s “commitment to European security is undiminished” after Brexit, citing collective efforts to bring Iran to the negotiating table and the united response to Russian aggression in Ukraine as areas of successful EU action in the past.

“In recent years, the European Union has helped achieve crucial foreign policy goals,” he said. “We want this EU role to continue after we leave. This is why, in addition to stronger relations with EU member states, we also envisage a strong UK-EU partnership on foreign and defence policy following our departure. This will allow us to continue our work in tackling the shared challenges we face worldwide.”

The new position paper strikes a more positive note about EU defence and foreign policy matters than expected, after Theresa May put security cooperation on the table as a bargaining chip to get a good trade deal when she wrote her letter to the EU triggering article 50 in March.

A senior Whitehall source said Nato would remain the “cornerstone of the UK’s defence” and Britain remains opposed to the idea of a collective EU army but cooperation with Brussels remained vital in the face of global threats to security.

The position paper does not deal with Home Office matters such as policing and crime cooperation, which will be covered by a separate document detailing whether the UK wants to stay in Europol and its approach to intelligence-sharing.

The defence document, due to be published in full on Tuesday, will signal a “willingness to partner with the EU in the face of ever-growing global threats”, including illegal migration, terrorism, cyber threats and state-based threats.

Britain’s aim will be to replicate a security partnership outside the EU “that is deeper than any other third country and that reflects our shared interest”, continuing with joint defence projects such as combating piracy off the Horn of Africa and work on the Eurofighter Typhoon aircraft.

The Brexit secretary, David Davis, said it was in the UK and EU’s mutual interest to work closely together.

“Today’s paper highlights Britain’s world-class diplomacy and defence capabilities, our leading contribution to international development, and our desire to continue to use these as part of a deep and special partnership with the EU,” he said.

The defence secretary, Michael Fallon, highlighted the UK’s military capacity, including the largest defence budget and navy in Europe, as well as troops and planes deployed on land, air and sea across the continent.

The government has already been at pains to reassure Nordic and Baltic countries that the UK’s approach to security in the region will not change after Brexit in the face of Russian aggression.

Labour MP Chris Bryant, a leading supporter of Open Britain, said the government’s intention to share a deep foreign policy and security relationship with the EU was welcome, but “makes a mockery of their threat to leave the EU with no deal”.

“Doing so would overnight end our security relationship with Europe, putting our citizens and theirs at risk. It is high time the government dropped its absurd no-deal threat,” he said.

“Finally, the Brexiteers seem to be waking up to how important the EU has been in advancing peace and security. The foreign secretary used to claim the EU played no role whatsoever in keeping us safe but today he praises its ‘crucial’ role in helping us to achieve our foreign policy goals.”