The shadow international development secretary, Kate Osamor, has resigned from her role amid accusations that she had misled the public over her son’s drug conviction.

Osamor, the Labour MP for Edmonton, north London, tweeted on Saturday to say she was stepping down from the shadow cabinet.

My Statement pic.twitter.com/w2J2Xrg2om — Kate Osamor🌹 || Labour & Co-op MP for Edmonton|| (@KateOsamor) December 1, 2018

Osamor’s 29-year-old son Ishmael is employed by her parliamentary office as a senior communications officer. He was handed a community sentence on 19 October after being caught with drugs worth £2,500 at Bestival in Dorset last year.

In a statement, Jeremy Corbyn said he accepted Osamor’s resignation and thanked her for her work as shadow international development secretary. “She brought a new dimension to the role by committing Labour to tackling global inequality as well as poverty,” he said. “I know Kate will take this time to support her family, work for her constituents and support our party’s efforts to rebuild Britain from the backbenches.”

Osamor had apparently previously claimed she knew nothing about Ishmael’s legal case until after the sentencing. It has since been reported that she must have been aware of the case before this because she had written to the trial judge asking for leniency.

Ishmael Osamor pleaded guilty to charges of possession with intent to supply cocaine, ecstasy, ketamine and cannabis on 18 September at Bournemouth crown court. It was accepted by the prosecution that Osamor was looking after the drugs for friends. Judge Stephen Climie said he had received five references in support of Osamor, which played a “significant” part in his decision to impose a community sentence of 200 hours of unpaid work.

The revelation that the MP may have known about the court case before the sentencing came after media organisations requested that the five references be released. While the judge declined to release the letters, he identified three of the authors as Ishmael Osamor, his partner and his mother.

Meanwhile, the National Union of Journalists condemned Osamor following allegations she threatened a reporter with a bat and threw a bucket of water at him.

Osamor told a reporter from the Times she should “smash his face in”, according to the newspaper.

She also reportedly told the reporter to “fuck off” and called police after accusing him of stalking. The journalist was attempting to speak to Osamor about the claims surrounding her son’s drug conviction.

Michelle Stanistreet, the NUJ’s general secretary, said: “Journalists, like any other workers, need to be able to go about their work without fear of threats or assault. It’s completely unacceptable to respond to legitimate press queries, however unwelcome they may be, with physical or verbal abuse.

“There is a disturbing and febrile international climate at the moment that is facilitating and legitimising the notion that it is open season on journalists – such insidious and dangerous beliefs, particularly when they emanate from public figures in positions of authority, have to be challenged at every turn.”

The Conservative MP Priti Patel called for the parliamentary standards commissioner to conduct an inquiry into the case and the continued employment of Osamor’s son in parliament.

“There are many questions outstanding here and Kate Osamor and the Labour party must make a full statement about what they knew about this case and why he continued to be employed on the public payroll at Westminster,” the former international development secretary told the Times.

Osamor was reported to parliament’s standards watchdog earlier this month, but on Twitter she said she had “done nothing wrong” and the referral was “politically motivated”.

In an open letter to the parliamentary commissioner for standards, the Conservative MP Anne-Marie Trevelyan said Osamor’s behaviour “failed to uphold” the code of conduct for MPs. “You do not need me to outline how serious drug offences are, and in this place we ought to treat them as such,” she said.