A RIGHT-wing think-tank has called Home Secretary Amber Rudd “deeply misguided” after she called for the government to be given a “back door” into encrypted networks following the attack at Westminster.

She called for the back doors to be built into systems so security services can access terrorists’ messages during investigations.

Rudd said she supported end-to-end encryption, offered by the likes of WhatsApp, but said security services must be able to eavesdrop when they have a warrant.

Khalid Masood reportedly used the app seconds before mowing down pedestrians at speed and storming the parliamentary estate armed with two knives last week. He killed policeman Keith Palmer before being shot dead by officers.

Although encryption makes it difficult for investigators to establish whether Masood was talking to an accomplice before Wednesday’s rampage, which left four dead, police said they believed he acted alone.

Sam Dumitriu, from the Adam Smith Institute, said: “Amber Rudd’s call on WhatsApp to give the government back-door access to your private communications is deeply misguided.

“It is mathematically impossible to build a back door for just the good guys. It means building a back door to your private messages for Putin’s favourite hacker Guccifer. It means opening up your private photos to perverts like the iCloud hacker. End-to-end encryption keeps us safe. Khalid Masood wasn’t even on MI5’s 3000-strong list of suspected jihadis.

“Ending end-to-end encryption would not have stopped the Westminster attack, but it would mean a free-for-all for cybercriminals and Putin’s hackers.”

WhatsApp said it had been assisting the police investigation.

“We are horrified at the attack carried out in London … and are co-operating with law enforcement as they continue their investigations,” said a spokeswoman.

Two men remain in custody over the attack – a 30-year-old was arrested in Birmingham on Sunday on suspicion of preparation of terrorist acts, making him the 12th person to be held over the plot.

A 58-year-old man also arrested in Birmingham remains in police custody after a series of raids across the country.

Officers have carried out a total of 15 searches at addresses in east London, south London, Brighton, Surrey, Carmarthenshire, Birmingham and Manchester.

A former Metropolitan Police deputy assistant commissioner branded Rudd’s call for access “draconian”. Lord Brian Paddick said: “The real question is, could lives have been saved in London last week if end-to-end encryption had been banned?

“All the evidence suggests that the answer is no.”

Downing Street would not give precise details of the action being sought from social media companies but insisted there was more they could do.

Rudd will aim to reach an agreement with them to improve on the current circumstances and allow law enforcement agencies to access content where necessary, said the Prime Minister’s official spokesman.

“How that is achieved is for the talks later in the week,” he said.

“These are companies which have fabulous technical expertise and where they can do more to assist, we would like them to do so.”