- Video report by ITV News Anglia's Serena Sandhu
The Conservative Party has been fined £15,000 for failing to report how it spent campaign money during the Clacton by-election in October 2014 following Douglas Carswell's defection to UKIP.
It's part of a record fine of £70,000 handed to the party over a series of issues with election expenses connected with two other by-elections, an election Battle Bus tour and the 2015 General Election.
In a separate investigation, police files have been handed to the Crown Prosecution Service over inquiries about candidate spending in a number of marginal constituencies.
Northamptonshire Police are among the forces that have referred the matter to the CPS to see if criminal charges should be made against MPs and their agents.
To ensure fairness between political parties there are limits to what each candidate can spend on campaigning to be elected.
The Clacton by-election in 2014 was triggered by the defection of the MP Douglas Carswell to UKIP.
During the by-election the Electoral Commission said there was a total declaration of £84,049.22 of which £12,314 was spending on an agent and other staff costs which was invoiced by the Conservative Party.
Of this £3,894.39 relates to spending on accommodation and administration.
The Electoral Commission found evidence supplied by Channel Four News that the Conservative Party booked accommodation in the Clacton area during the by-election.
- Lifehouse Spa - 290 nights between 4 September and 11 October 2014 - cost unknown
- Premier Inn - 71 nights between 9 September and 1 October 2014 at a cost of £6,582.86
The Electoral Commission found that all accommodation costs for staff and volunteers should have been declared as by-election campaign expenses because it was "to facilitate those individuals' work on the respective by-election campaigns.
This money would not have been spent otherwise."
The Conservative party said it used a formula to work out how to apportion costs between local and national campaigns.
However the Electoral Commission said it was unclear how the proportion was calculated and correct accounting records had not been kept as required by election law.
The Commission said in its report that the only credible purpose was to work on the by-election campaigns therefore it was "not satisfied" the proportion of costs was a "true reflection."
A Conservative Party spokesman said it would pay the fines imposed without argument.