Britain's intelligence expertise may be "too precious" to use as a bargaining tool in the upcoming Brexit talks, experts said, after a terror attack in London highlighted the need for continued European security cooperation.

The suggestion that Britain could use security to negotiate with Brussels came following US President Donald Trump's election and his calls for a more isolationist foreign policy.

"If the US does adopt a more isolationist stance, then ongoing security cooperation with the UK becomes more valuable," the Institute for Government said in November.

"This could strengthen the UK’s negotiating hand in Brexit talks, as it could use the promise of ongoing cooperation on security measures to extract a more favourable deal from the EU," the think tank said in a report.

Prime Minister Theresa May in a speech in January talked up the importance of Britain's intelligence to the rest of Europe, suggesting it could be part of the negotiations.

"Our intelligence capabilities -- unique in Europe –-- have already saved countless lives in very many terrorist plots that have been thwarted in countries across our continent," she said.

But using security as a negotiating chip would entail the possibility of withholding cooperation -- an unthinkable prospect for most analysts in an era of shared threats.

The attack in London last week in which 52-year-old Khalid Masood -- said by the Islamic State group to be one of its "soldiers" -- killed four people and injured dozens more outside Britain's parliament underlined that fact.

"It's quite difficult to see how you might actually use that as a bargaining lever," James de Waal, a former diplomat at the London-based Chatham House, told AFP.

De Waal also emphasised that "a lot of the security cooperation relationships are not done through the EU, they're done on a bilateral basis".

David Galbreath, professor of international security at the University of Bath, also said Brexit would not hamper intelligence cooperation, pointing out that Britain was "a conduit for the Americans to share with the Europeans".

- 'Very important time' -

Politicians from May's own Conservative Party have also called for the issue to be taken off the table. 

"The seriousness of the matter and the degree of mutual interest give weight to the suggestion that this aspect of negotiations be separated firmly from others, it is too precious to be left vulnerable to tactical bargaining," Conservative MP Bob Neill, chair of the House of Commons Judicial Affairs Committee, said last week. 

Europol boss Rob Wainwright earlier this month told a parliamentary committee that there was "concern" in the European police community "that British expertise and even leadership is not lost at a very important time" of heightened terror threat.

British police too have stressed the importance of maintaining close ties with continental colleagues, with outgoing Metropolitan Police chief Bernard Hogan-Howe insisting "we want to keep a good relationship with Europe".

Shortly before last June's Brexit referendum,former head of domestic intelligence agency MI5 Eliza Manningham-Buller, warned of the dangers of leaving the EU. 

"If Europe is weakened by our departure, it will weaken our security," she said. 

When asked by the AFP, Britain's interior ministry vowed that London would "discuss with the EU and member states how best to continue cooperating on security, law enforcement and criminal justice.

"We're clear that we'll do what is necessary to keep our people safe," the ministry said.

Source; AFP