Russia unleashed an “extensive” disinformation operation in Britain after the Salisbury spy attack, with thousands of suspected robotic accounts spreading doubt and conspiracy on the internet, officials believe.

It is understood that an estimated 2,800 such online accounts are suspected of posting material about the attempted murder of Sergei Skripal and his daughter Yulia in Salisbury, according to monitoring reports prepared for the government. Messages posted by the suspect accounts are thought to have been interacted with 75 million times and to have reached at least 7.5 million people in Britain.

A key aim of the accounts appears to be to cast doubt on Theresa May’s assessment that the Kremlin is responsible for the nerve agent attack on March 4 and to turn people in