A man has admitted sending fake anthrax to a string of female politicians, including the Conservative MP Chloe Smith and the Labour MP Emma Reynolds.

Richard Hayes, 40, of no fixed abode, was arrested in Barnstaple, north Devon, on 18 July by counter-terrorism officers. He appeared via video link at Exeter crown court on Thursday and admitted 16 charges of making a noxious substance hoax, contrary to section 114 of the Anti-Terrorism, Crime and Security Act 2001.

The charges state that Hayes sent white powder and packages marked “anthrax” from Exeter to the offices of MPs and local councillors.

The judge, Peter Johnson, adjourned the case for reports to be carried out but warned Hayes he faced a lengthy custodial sentence.

Hayes was caught when his DNA was taken by police after he was cautioned last December for harassing a woman. The sample led police to the person who between 2011 and 2014 had been sending white powder to female MPs and other politicians. He did not appear to target politicians of certain parties but his victims were almost all women.

The charge sheet read that on various dates he “sent a substance, namely white powder, from one place to another intending to induce in a person anywhere in the world a belief that it is likely to be or contain a noxious substance or other noxious things and thereby endanger human life or create a serious risk to human health”.

Other politicians targeted included the Liberal Democrat Welsh assembly member Kirsty Williams, and Heidi Alexander, the deputy mayor for transport in London. He also sent packages to several female Exeter councillors.

Hayes’s barrister asked for a pre-sentence and psychiatric report before he is sentenced in November. Ed Bailey said reports would help “explore his motivation to commit such serious crimes … He has pleaded guilty to 16 very serious offences and a custodial sentence is inevitable.”

Full details of the case were not detailed in court but Rachel Drake, prosecuting, described it as unusual.

The court heard Hayes, who had no previous convictions, was cautioned last December for harassing a female partner.

Section 114 of the Anti-Terrorism Act created a new offence of hoaxing, which involves noxious substances or things. The essence of the hoax is that the substance used is not the substance it seems to be.

It brings legislation into line with bomb hoaxes as a terrorist weapon. For example, scattering white powder in a public place or spraying water droplets on an underground train could fall within the scope of the new offence.