The Crown Prosecution Service will not be taking any action following investigations by police forces across the country, including Northamptonshire, over spending on an election "battle bus".
The battle bus visited the Northampton North constituency ahead of the General Election in 2015 to support the campaign by Michael Ellis.
A nationwide investigation was launched after complaints in relation to how the expenditure was declared by the national Conservative Party. Mr Ellis consistently denied any wrong-doing and said the local association was following the national party's guidelines.
Today, the CPS said no further action would be taken following the investigation.
Nick Vamos, CPS head of special crime, said: "We have considered files of evidence from 14 police forces in respect of allegations relating to Conservative Party candidates' expenditure during the 2015 General Election campaign.
"We considered whether candidates and election agents working in constituencies that were visited by the Party's 'Battle Bus' may have committed a criminal offence by not declaring related expenditure on their local returns. Instead, as the Electoral Commission found in its report, these costs were recorded as national expenditure by the Party.
"We reviewed the files in accordance with the Code for Crown Prosecutors and have concluded the tests in the Code are not met and no criminal charges have been authorised.
"The Representation of the People Act makes it a technical offence for an election agent to fail to deliver a true return. By omitting any 'Battle Bus' costs, the returns may have been inaccurate. However, it is clear agents were told by Conservative Party headquarters that the costs were part of the national campaign and it would not be possible to prove any agent acted knowingly or dishonestly. Therefore we have concluded it is not in the public interest to charge anyone referred to us with this offence."
In response, Conservative Party Chairman Patrick McLoughlin said: "After a very thorough investigation, we are pleased that the legal authorities have confirmed what we believed was the case all along: that these Conservative candidates did nothing wrong. These were politically motivated and unfounded complaints that have wasted police time. We are glad that this matter is finally resolved.
"A number of false and malicious claims continue to be spread on the internet. People should be aware that making false claims about a candidate's personal character and conduct is an electoral offence, as well as being defamatory.
"Notwithstanding these false claims, Conservatives want to strengthen election rules to safeguard electoral integrity - in light of the real and proven cases of electoral fraud exposed in Tower Hamlets in 2015."
Mr Ellis, who is Conservative Parliamentary Candidate for Northampton North in next month's General Election, said: "My focus has been, and continues to be, the people of Northampton North, and doing everything I can to ensure a Conservative victory in Northampton North."