A Luton-based woman who kept secret her brother’s plot to kill people in a terrorist attack in London has been sentenced to two years in jail at the Woolwich Crown Court, Scotland Yard said on Wednesday.

A six-and-a-half-month, covert investigation by the force’s Counter Terrorism Command identified that Sneha Chowdhury, 26, knew that her brother, Mohuissunnath Chowdhury, 29, was planning to carry out a terrorist attack.

Her sentence was suspended for two years, and given a 60-day rehabilitation order, the police said. She was previously found guilty of one count of failing to disclose information regarding terrorist activity.

Her brother Mohuissunnath, who was previously sentenced to life imprisonment, was recorded at home telling his sister that he was “doing another attack”, and asking her for help to practice stabbing people – information which she did not report to police.

Commander Richard Smith of the Counter Terrorism Command, said: “There is no acceptable reason for listening to someone say they are planning to kill innocent people, and watching them practice how they will do that, then not reporting it to police”.

“Sneha Chowdhury willfully kept her brother’s horrific secret, but not every case has to end this way. If relatives report indications that a loved one is becoming radicalised early on, there is an opportunity for authorities to intervene and help them before they become too deeply entrenched. All it takes is a phone call.”

The Woolwich Crown Court jury had earlier found her brother guilty of preparation of acts of terrorism, for a plot to carry out an attack at a tourist hotspot in London; dissemination of a terrorist publication; and possession of information useful to terrorism, for having a guide to carrying out terror attacks on his phone.

He was subsequently sentenced to life imprisonment on July 9, and must serve a minimum of 25 years in prison.