Jerry Hayes, a former Conservative MP and barrister, said the rules were clear and that “the police are not entitled to trawl through all calls and social media as a matter of course”.

Mr Hayes was reacting to an outcry over new police forms that must be signed by people reporting rape and which allow detectives to seize data from their electronic devices.

Failure to hand over the data mean the cases could be dropped and two women are undertaking a legal challenge to the introduction of the forms.

“Asking a complainant’s permission to interrogate their phones and social media is common sense and in the interests of a fair trial,” Mr Hayes said.

He told The Times that “warning that failing to co-operate might lead to the abandonment of a trial is pretty basic”.

He said: “The defence would ask for disclosure and if it is refused, alarm bells would start to ring.”

Paul Morris, of BCL Solicitors, said the new forms did not change the statutory test for disclosure as enshrined in the Criminal Procedure and Investigations Act 1996.

The act requires the prosecution to disclose its case to the defence along with any material capable of undermining the prosecution’s case or assisting that of the defence.

Richard Atkinson, co-chairman of the Criminal Law Committee of the Law Society, said there was much “misinformation” about the new forms.

“Being up front about the need for proper disclosure is important,” he said.

“People need to understand that the data will only be disclosed to the defendant if it meets the disclosure test of assisting the defence case or undermining the prosecution.”

Thomas Ross QC

Speaking to Scottish Legal News, advocate Thomas Ross QC said that use of phone data should be determined on a case-by-case basis to avoid abuse of police powers and cited a recent Scottish case where the issue arose.

“I have very recent experience of a case where consent was a material issue – and the complainer had sent text messages to the accused in the most graphic terms which completely contradicted the position that she had adopted in her police statements.

“Surely nobody would suggest that the jury should be unaware of those messages? That said, I disagree with a policy of seeking consent in all cases. In most cases, nobody is suggesting that electronic communications exist that have a bearing upon the issues – in those cases it would be a clear abuse of police powers to interrogate the complainer’s telephone.

“Investigative methods usually require to be case-specific to be successful – this area is no different.”