The commission also highlighted the Tories had made "numerous failures" in reporting its expenses for the Rochester and Strood by-election in 2014, in which Mark Reckless, who defected from the Conservatives to Ukip, defeated Kelly Tolhurst - a vote that would then be reversed less than 12 months later in the general election.
The investigation was targeted at the national party but had potentially even more serious implications for more than 20 Conservative MPs who are under police investigation for alleged election fraud related to under-declared spending on their local campaigns.
But a CPS spokesman said it had received files from: Avon & Somerset, Cumbria, Derbyshire, Devon & Cornwall, Gloucestershire, Greater Manchester, Lincolnshire, the Metropolitan Police, Northamptonshire, Nottinghamshire and West Yorkshire police.
It has also referred to police the Tories' former treasurer Simon Day, who had a legal duty to ensure accurate accounts.
"Officers from Kent Police continue to work with the Electoral Commission as the investigation continues".
"Lancashire Police interviewed me and they saw fit not to take it any further", he said.
As we have consistently said, the local agents of Conservative candidates correctly declared all local spending in the 2015 general election.
Will Quince, the MP for Colchester, said he had been told by Essex Police he faced no further action after voluntarily attending an interview under caution last January.
The row centres on the Tories' use of the election battle bus to campaign in key seats, and whether spending on hotels and campaign material was incorrectly registered as national spending, which has much higher limits than local spending.
The Conservative Party has complied fully with the Electoral Commission's investigation since it began more than a year ago and will pay the fines they have imposed.
"We need to make sure that all parties get that through the system and actually we have a fair and satisfactory conclusion which means that those MPs who did nothing wrong, whose election expenses are absolutely as the rest of ours were, are not tarnished".
It comes just days after reports emerged of Mr Mackinlay being questioned for six hours under caution by Kent Police last week in relation to his expenses.
The Conservative party said it accepted the Electoral Commission findings but attempted to downplay them as a "reporting error" and claimed "political parties of all colours have made reporting mistakes from time to time".
The Conservatives deny that Mr Timothy worked directly on the Thanet South campaign.
Karl McCartney, MP for Lincoln and one of those under investigation, wrote a bombshell email to the party chairman Patrick McLoughlin attacking the party's handling of the controversy.
"This matter is now subject to assessment by officers from the Special Enquiry Team".