Nick Clegg will accuse Theresa May of putting the safety of Britons at risk after Brexit, after she failed to explain how the police will retain access to EU anti-terror information.

The former Liberal Democrat leader will condemn the Prime Minister for vowing to pull the UK out of the jurisdiction of the European Court of Justice (ECJ) – whatever the cost.

Outside the ECJ, Britain is likely to lose the right to share data through the Europol enforcement agency and the Schengen information system, which holds the names of 8,000 suspected terror suspects.

On Monday, Ms May was asked if she had an “alternative plan” to keep the national security data flowing but simply referred vaguely to trying to agree “appropriate oversight” of the information.

Instead, the Prime Minister vowed: “I am very clear that the European Court of Justice and its jurisdiction in the UK is going to be ended”.

Delivering a major speech on the threats posed by Brexit, Mr Clegg will say: “How will Britain be kept safe after Brexit?

“Theresa May has vowed to pull Britain out of the jurisdiction of the European Court of Justice, a decision which means we would no longer have access to vital EU-wide databases of criminal activity.

“So where are the contingency plans when our police forces find themselves unable to check the databases of 28 EU countries at the touch of a button? If only she would deign to tell us, then maybe we could judge.”

Mr Clegg, now the Lib Dems Brexit spokesman, will also accuse the Prime Minister of a breathtaking U-turn on the security implications of EU withdrawal.

“Just last year, a not-so-distant era when Theresa May made perfectly rational arguments against leaving Europe, she warned that being in the UK makes us “more secure from crime and terrorism”,” Mr Clegg will add.

At the weekend, The Independent revealed that data experts fear the Government is failing to recognise the danger to businesses and the fight against terrorism from losing information-sharing rights.

Britain risks a wait of up to three years to be granted an “adequacy decision” from Brussels, threatening to stop the flow of data immediately unless a temporary deal can be struck.

Crucially, separate agreements may have to be struck with individual police forces and intelligence services – with the danger that vital information will “fall between the cracks”, one expert said.

Furthermore, Sir Julian King, the European commissioner responsible for security, has also warned Britain will have to give way on ECJ oversight.

In April, a Home Office minister, Baroness Williams of Trafford, was unable to say what “the transition arrangements might look like”, when quizzed by a House of Lords committee.