Rupert Lowe, the MP for Great Yarmouth, will not face criminal charges in relation to an allegation of threats, the Crown Prosecution Service has said.
Lowe was elected as a Reform UK MP in last year's general election but was suspended by the party in March, amid claims of threats towards the party's chairman, Zia Yusuf.
Malcolm McHaffie, head of the CPS, said it made the decision not to press charges "following a thorough and detailed review of the evidence".
"Having considered a number of witness statements, we have concluded that there is insufficient evidence to provide a realistic prospect of conviction," he said.
In a statement on X, Lowe said the Metropolitan Police were dropping their investigation into "false allegations" and accused Reform of carrying out a "brutal smear campaign".
"For the sin of asking legitimate questions about the party's direction, policies and leadership, I was vilified and targeted," he said.
Lowe, who now sits as an independent MP, also fiercely attacked his former party's leader Nigel Farage, calling him a "a coward and a viper".