The self-styled adviser to former defence secretary Liam Fox will not face criminal charges, prosecutors have announced.
Adam Werritty was under investigation after describing himself as Mr Fox's adviser on business cards and allegedly accepting donations as part of that role.
Andrew Penhale from the Crown Prosecution Service said: "Following an investigation by City of London Police, we have decided that there is insufficient evidence to prosecute Mr Adam Werritty for any alleged offences.
"The matters referred to us involved the alleged misuse of Mr Werritty's business cards and of funds donated to his business.
"These are matters which have been widely reported. In accordance with the Code for Crown Prosecutors, we have advised City of London Police that there is insufficient evidence to provide a realistic prospect of conviction."
Dr Fox resigned last year after being found guilty of breaching the ministerial code over his relationship with Mr Werritty, whom he met 40 times in the Ministry of Defence and on trips abroad.
Speaking in an interview with BBC Radio Bristol last year, he said: "My mistake there was to effectively allow someone to function as an independent adviser and that is not allowed under the Ministerial Code. I should have kept a better separation there - with hindsight, it seems easy."
In a statement issued to the Daily Mail, Mr Werritty said: "While much of last autumn's media coverage was often short on detail and substance, and in a minority of cases little more than innuendo, a serious allegation, of fraud, was made against me.
"I have always maintained that this allegation was baseless so I naturally feel vindicated, but unsurprised by the CPS's decision.
"I owe a big thank you to my family and close friends for their unwavering support over the last 12 months leading up to today's outcome."