A mother and her two daughters have been found guilty of planning a terrorist attack in the UK in Britain’s first all-female terrorist plot.

Safaa Boular, 18, was found guilty for preparation of terrorist acts on Monday at the Old Bailey court in central London. Her mother Mina Dich, 44, and older sister Rizlaine Boular, 22, had already pleaded guilty.

Security services started investigating the two sisters in August 2016 after officers spoke to Safaa after her return from a trip to Morocco. Then just 16, Safaa indicated she was planning to travel to Syria to live in areas controlled by the so-called Islamic State.

Officers also seized mobiles phones and digital devices on which they found conversations between Safaa and a UK national who was fighting for ISIS in Syria. The two were planning to marry and had discussed Safaa wearing a suicide belt.

The teenager was arrested and charged in April 2017.

While in custody, she remained in contact with her mother and sister and shifted her attention to planning an attack in the UK. Over phone conversations recorded by intelligence services, the three women discussed having a ‘tea party,’ their code word for the attack.

Days later, officers followed Mina and Rizlaine as they drove through Westminster, past a number of major landmarks, in what security services believe was a reconnaissance trip. They also bought kitchen knives in a local supermarket.

Mina Dich Metropolitan Police

Rizlaine and Mina were arrested on April 27, 2017, the day of their scheduled attack.

"All three women were filled with hate and toxic ideology and were determined to carry out a terrorist attack. Had they been successful, it could well have resulted in people being killed or seriously injured,” The Metropolitan deputy assistant commissioner Dean Haydon said in a statement.

Mina and Rizlaine will be sentenced on June 15. Safaa is remanded in custody and will be sentenced on a date to be confirmed.