British intelligence held in eu security systems would have to be deleted immediately in the event of a no-deal brexit, imperilling wanted alerts triggered by uk spies and police, a former brussels security chief has warned.

Julian king who stepped down in november as the uks last european commissioner said that while post-brexit security arrangements had received less attention than negotiations over trade and economics, being unplugged from eu law enforcement mechanisms in the new year would have a significant impact on efforts to catch terrorists and criminals moving across the continent.

One of the major sticking points in discussions between london and brussels is how to manage data-sharing for law enforcement once britains post-brexit transition period expires on december 31. in particular, uk police and security agencies are keen to maintain access to sis ii, an eu database with real-time crime alerts, the european criminal records information system, and the so-called prm information-sharing arrangements for dna and fingerprints.

The latest round of eu-uk talks, which got under way on tuesday in brussels, includes four sessions on law enforcement co-operation.

Sir julian, who was speaking at an event hosted by the royal united services institute, an uk defence think-tank, in london on tuesday, said failure to agree a deal after brexit would affect existing information held in eu-wide databases as well as future intelligence co-operation.

Uk data held in eu systems could, indeed would, be deleted if there was no data adequacy arrangement and even if there were such an arrangement, data that was time-limited...would also be deleted from eu systems, he said. so its not only about being unplugged, its also about the information that has been shared being struck out of eu systems.

The former diplomat said the loss of this data this would have an immediate impact. the exchange of sis data helps track down offenders who flee overseas, as well as preventing foreign offenders from slipping across the border into the uk. this system has already helped intelligence officials track the movements of foreign jihadis returning from fighting alongside isis in syria and iraq.

John scarlett, former chief of the uks secret intelligence service, known as mi6, said counter-terrorism work would be particularly vulnerable if security co-operation was eroded. if theres a weakening of data capability and data exchange capability and subsequently investigative capability in the eu and or the uk, then that clearly...potentially weakens our ability to respond to the islamic jihadi threat, he told the rusi event.

Sir john added that tracking movements, crossing frontiers, knowing where people are at any one time was fundamental to effective counter-terrorism work.

Brussels has told the uk that access to sis ii is off the table for legal reasons no country that is outside both the eu and europes schengen free travel area has access. but the eu has said it is open to exploring ways to continue sharingprm data, provided strong data protection safeguards are in place.

However, the question of how to guarantee data protection has bedevilled talks on the two sides future security partnership.

Brussels has said future co-operation will depend on it taking a unilateral adequacy decision that britains data privacy standards are as robust as the eus own and that its evaluation of this is ongoing. the uk has pushed instead for data protection clauses to be enshrined in the future-relationship agreement that boris johnsons government is negotiating with the eu.

The eu has also had to contend with the fallout of a july ruling in the european court of justice that invalidated a transatlantic agreement used by about 5,000 companies to transfer data from the eu to the us. the court backed arguments from max schrems, a data-privacy activist, that the arrangement known as privacy shield offered insufficient legal redress against potential misuse of personal information by us authorities.

Eu officials acknowledged to the financial times that the court decision had raised the bar the eu would have to clear to justify data-sharing with the uk, further complicating talks.

The two sides have also been at loggerheads over britains reluctance to commit to respecting the european convention on human rights, something the eu sees as an essential precondition of the future partnership.