A man with paranoid schizophrenia who pushed a 91-year-old on to London Underground tracks has been jailed for life by a judge who described him as “a grave and enduring risk to the public”.

Paul Crossley shoved Sir Robert Malpas on to the rails at Marble Arch station on 27 April last year, minutes after attempting to do the same to another man at Tottenham Court Road.

Crossley, 47, from Leyton, east London, was sentenced at the Old Bailey on Monday, with a stipulation that he must serve a minimum of 12 years before he can be released on parole.

He was found guilty of two charges of attempted murder in October but sentencing was delayed for eight months so that detailed psychiatric reports could be prepared.

Malpas, a former co-chairman of Eurotunnel, was saved by Riyad El Hussani, a bystander, who pulled him up shortly before a train was due to arrive. He sustained a broken pelvis and a cut to the head that required 12 stitches, and spent more than a week in hospital following the attack.

Facebook Twitter Pinterest Paul Crossley, 47, said he had taken crack cocaine the day before the attack and felt paranoid. Photograph: British Transport Police/PA

A few minutes before, Crossley had tried to push Tobias French on to tracks as the latter was making his way home. French fought him off, later saying that he had only been able to maintain his balance due to his background as a professional sportsman.

Crossley was chased and caught by members of the public after pushing Malpas. He later said he had taken £600 of crack cocaine on the day before the attack and had begun to feel paranoid.

The recorder of London, Judge Nicholas Hilliard QC, told Crossley that it was beyond doubt that he was “reducing the efficacy” of medication for his mental illness because of the drugs he was taking.

“You said in evidence that taking crack cocaine can make your schizophrenia worse and that it was not a good idea for you to take it,” said the judge, who added that he was satisfied that Crossley’s paranoia could be described as anxiety, and that paranoia was also a symptom of crack cocaine.

He told him: “You may seek to present symptoms as an excuse. I am satisfied that paranoid schizophrenia was not the driving force, but drug abuse and your natural tendency to aggression.

“In my judgment your culpability for this offence remains high such that punishment is necessary and a hospital order would not be suitable. You present a grave and enduring risk to the public.”

Crossley had told jurors that he picked people at random and did not mean to kill them.

The court heard that he had told Dr Anneka John-Kamen, a psychiatrist, that he had gone to the West End after hearing the song West End Girls on the radio, believing it was giving him instructions. Hilliard dismissed the significance of this.

Crossley had also told John-Kamen that he remembered thinking he was going to “hurt someone” and was anxious because he had been threatened by people he owed money.

The defendant also claimed he had only meant to scare French and to push Malpas on to the floor. He was in breach of two suspended sentences at the time he tried to kill the two men, his trial was told.

In September 2016 he pleaded guilty to sexual assault after he groped a care worker who came into his room to give him his medication.