The Conservatives and the Liberal Democrats are demanding the Labour government publish the evidence it submitted in the now-collapsed case against two people accused of spying for China.

It follows another public intervention from the Crown Prosecution Service (CPS), which has made clear it would not stand in the way if ministers chose to put their evidence in the public domain.

On Tuesday, senior government figures had suggested that the CPS had told them to do so would be “inappropriate”.

Prosecutors unexpectedly dropped the case against Christopher Cash and Christopher Berry last month, prompting criticism from ministers and MPs. Both men deny the allegations.

The director of public prosecutions said the case collapsed because evidence could not be obtained from the government referring to China as a national security threat.

This row within a row relates to the three witness statements submitted by Deputy National Security Adviser Matthew Collins, on whether China had been regarded as a threat at the time of the alleged offences under the previous Conservative government.

The CPS has now said: “The statements were provided to us for the purpose of criminal proceedings which are now over.

“The material contained in them is not ours, and it is a matter for the government, independently of the CPS, to consider whether or not to make that material public.”

Mr Cash, a former parliamentary researcher, and Mr Berry were charged under the Official Secrets Act in April 2024, when the Conservatives were in power.

They were accused of gathering and providing information prejudicial to the safety and interests of the state between December 2021 and February 2023.

Shadow Home Secretary Chris Philp told the BBC: “The government should now urgently release Matt Collins’s witness statements and the correspondence around them in the interests of full transparency.

“Since this evidence would have been cross-examined in court, it cannot be secret.

“Otherwise, there will be legitimate questions about what exactly the government is hiding.”

Liberal Democrat Foreign Affairs Spokesperson Calum Miller also called on Labour to release the full witness statements.

“If ministers have nothing to hide they have nothing to fear,” Miller said. “Failure to come clean will just confirm people’s suspicions of a cover-up and that ministers are more worried about cosying up to China than protecting our national security.”

On Sunday, Conservative leader Kemi Badenoch wrote to the prime minister asking him to address “unanswered” questions about the collapsed case.

In her letter, Badenoch accused Sir Keir Starmer, or his ministers, of being “too weak to stand up to Beijing on a crucial matter of national security”, claiming the government had sought to “appease China”.

There is every possibility Sir Keir will for the first time face sustained public scrutiny on the case on Wednesday, when he appears at the first Prime Minister’s Question time for several weeks, after the parliamentary recess for party conferences.

The Labour leader previously said ministers could only draw on the last government’s assessment of China, in which the country was called an “epoch-defining challenge”, and his government has maintained it is “frustrated” the trial collapsed.

The Tories have asked the CPS if it would be able to restart prosecutions against the two men, if new evidence is brought forward by the government declaring China a threat to national security.

But there is an exceptionally high bar to prosecuting someone for a second time after an acquittal in court – and it is not possible to do so for people charged under the Official Secrets Act.

That protection against what is known as “double jeopardy” is a basic legal principle that has existed for 800 years.