The Met Police is investigating letters sent to two people containing threats and “vile racist and transphobic language”.
The force said its Counter Terrorism Command was leading the investigation into the messages, sent from a group calling itself the National Action London Cell, due to the “potential involvement of a proscribed group”.
On Monday, political activist and commentator Dr Shola Mos-Shogbamimu shared an image of a letter, signed from the London Cell, which contained racist abuse and threats to her life and the lives of her family.
Fascist group National Action, founded in 2013, has been a proscribed organisation in the UK under the Terrorism Act 2000 since December 2016.
Following the ban, it split into regional factions with bases around the country.
They don’t consider killing me ‘murder’, they call it an ‘execution’— Shola Mos-Shogbamimu
The Met said it was first made aware of the letters as a result of Twitter posts on Monday and that an investigation was under way.
Officers have contacted the victims to request statements and offer support.
On Monday, Dr Mos-Shogbamimu, who regularly appears on TV debating issues including diversity and women’s rights, tweeted: “I have received ‘a serious threat from National Action London’ notifying me of their ‘intention to kill’ me & my family.
“They name my husband & home address. They don’t consider killing me ‘murder’ they call it an ‘execution’. This letter was through my front door.”
She added: “This is Britain.”
An image of the letter shared by Dr Mos-Shogbamimu showed it to contain a series of racial slurs relating to her African heritage.
She added that she had been receiving calls on her mobile that were ended by the caller as soon as she picked up.
In response to her post, Labour MP Jess Phillips said: “All my love Shola, please shout if I can help.”
No arrest has been made and enquiries continue.
