Image copyright PA

Britain will not seek to obstruct European efforts to develop closer defence co-operation after Brexit, Boris Johnson has said.

In a speech in London, the foreign secretary said: "If they want to do that, fine," but said countries should ensure they met their Nato commitments.

Defence Secretary Michael Fallon has previously said the UK would oppose the move because it could "undermine" Nato.

France and Germany have made the case for increased military co-operation.

In March 2015, European Commission President Jean-Claude Juncker declared a common European army was needed to face up to Russia and other threats. In August 2016, the leaders of the Czech Republic and Hungary said a joint European army was needed to bolster security in the EU. The idea is thought to have been given impetus by the UK's Brexit vote.

'Dog in the manger'

Proposals under discussion in Brussels include a new joint EU military command, expanding the EU's peacekeeping missions and joint development of military hardware like helicopters and drones - although Germany and France say it is about increased co-operation, not an EU army.

Speaking at Chatham House, the Royal Institute of International Affairs, Mr Johnson said: "We want a strong EU and we want a strong relationship between a strong UK and a strong EU," said Mr Johnson.

Image copyright Getty Images Image caption France and Germany want joint development of military hardware such as helicopters

"It is no part of our agenda to seek to undermine or to be dog-in-the-mangerish about the EU.

"There's a conversation going on now about the EU's desire to build a common security and defence policy and a new architecture for that. If they want to do that, fine - obviously they should also spend 2% of their GDP on defence.

"We are not there to block or to impede further steps towards EU integration if that is what they desire. We are there to support and to build a strong, thick relationship."

But in September, his cabinet colleague Mr Fallon said Nato "must remain the cornerstone of our defence and the defence of Europe" adding: "We're going to continue to oppose any idea of an EU army, or an EU army headquarters which would simply undermine Nato."

'We don't agree'

Asked about Mr Johnson's comments, a Downing Street spokesman said the UK had been "clear... that any EU defence and security proposals that may come forward should complement Nato and not duplicate Nato."

"We remain members of the EU at the moment and we have made clear we don't agree with a European defence force," he added.

In his speech, Mr Johnson also committed Britain to the concept of collective Nato defence ie "an attack on any one member shall be considered an attack against them all" but said he backed US President-elect Donald Trump's call for Nato countries to spend more on defence.

"President-elect Donald Trump has a point. It cannot be justified that one Nato ally, America, accounts for about 70% of the alliance's defence spending while the other 27 countries manage only 30% between them."

He said every Nato member should meet the agreed target of spending 2% of GDP on defence, and 20% of their defence budget on new equipment.

During his election campaign, Mr Trump was critical of Nato, describing the Western military alliance as obsolete.

He suggested that the US would think twice about coming to the aid of any Nato ally under attack if it had not paid its "fair share".