Theresa May’s email account was among those targeted by Iranian hackers Matt Dunham/Associated Press

Iran carried out a “brute force” cyberattack on parliament that hit dozens of MPs this summer, according to a secret intelligence assessment.

Some 9,000 email accounts, including those belonging to Theresa May and other cabinet ministers, were subjected to a sustained attack on June 23. Ninety accounts were compromised.

Russia was initially blamed but investigators have traced the attack to the Tehran regime, The Times can reveal. It is believed to be Iran’s first significant act of cyberwarfare on Britain and underlines its emergence as one of the world’s biggest cyberpowers.

The timing of the revelation is awkward for Mrs May as she seeks to persuade President Trump not to abandon the Iran nuclear deal.

He said yesterday that he would refuse to certify the…