The veteran MP launched an outspoken attack on the Labour leadership five months after she was booted out of the party amid an anti-semitism row.
Abbott, the MP for Hackney North and Stoke Newington, lost the Labour whip in April after she wrote a letter to The Observer claiming Jewish, Irish and Traveller people have never been “subject to racism”.
Starmer later described her comments as “anti-semitic” and accused her or arguing there is a “hierarchy of racism”.
The former shadow home secretary apologised “unreservedly” for any “anguish” and said she withdrew the comments.
At the time, Labour said it was launching an investigation into the affair.
But in a statement published on X (formerly Twitter) today, Abbott said the probe was “fraudulent”.
She said: “I was told by the chief whip to ‘actively engage’ with an investigation.
“But the Labour whips are no longer involved - it is now run entirely out of the Labour Party HQ, which reports to Keir Starmer — and there is no investigation.
“This is the same Keir Starmer who almost immediately pronounced my guilt publicly. This completely undermines any idea that there is fairness or any natural justice. It is procedurally improper.”
She added: “The Labour Party has not charged me with anti-semitism because they know it is untrue. As someone who has fought all forms of racism all my life, I would consider it a very serious allegation. Instead, it has been used to smear me, my reputation, and decades of anti-racist work.”
Abbott said she had remained silent until now “in the hope that some sense of decency, and recognition of the tenets of natural justice might prevail”.
But she said: “The Labour Party disciplinary machine has clearly shown that it has little interest in either.”
Abbott also accused the Labour leadership of seizing control of her local constituency party.
“In effect, the Labour apparatus has decapitated the elected leadership of the constituency party to install its own, hand-picked personnel and replace me as the candidate prior to the next election,” she said.
“This is what some have clearly wanted all along. Taken together, the procedural impropriety, Starmer’s pronouncement of my guilt, the four-month delay in the investigation, the repeated refusal to try to reach any accommodation, all point in the direction that the verdict has already been reached.”
The MP, who was first elected 40 years ago, added: “I am the longest serving black MP. Yet there is a widespread sentiment that as a black woman, and someone on the left of the Labour Party, that I will not get a fair hearing from this Labour leadership.”
In a statement, left-wing campaign group Momentum said: “The Labour leadership’s treatment of Diane Abbott is nothing short of disgraceful, and is an insult both to Diane and to Labour Party members in Hackney, who voted overwhelmingly to reselect Diane.
“If there is any semblance of democracy and due process in Starmer’s Labour, a fair and proper process should rapidly be concluded and the whip restored.”
A Labour Party spokesperson said: “The Labour Party rightly expects the highest standards of behaviour from its elected representatives, and has introduced an independent complaints process to investigate cases. We do not give a running commentary on ongoing investigations.”