The Liberal Democrats have been slapped with a £20,000 ($25,205) fine and face a police probe for failing to declare just under £185,000 of spending at the 2015 general election, the Electoral Commission announced on Wednesday (7 December).
The watchdog issued the maximum penalty after finding 307 payments were missing from the party's spending return "without a reasonable excuse". The Commission also discovered invoices supporting 122 out of the 307 payments were missing from the return.
"Our investigation uncovered systemic failures in ensuring that the rules were being followed," said Bob Posner, the director of regulation and legal counsel at the Commission.
"The party and its officers co-operated fully throughout the investigation.
"However, this is an experienced party that failed to meet the basic requirements of the law, and cases like this undermine voters' confidence in our political finance system. This is why we have applied the highest financial penalty available to us."
The watchdog has also notified the Metropolitan Police of a possible criminal offence, should party campaigns officer have "knowingly or recklessly signed a false declaration" in relation to the spending.
A Metropolitan Police spokesperson said: "We can confirm that officers from the Special Enquiry Team are currently assessing an allegation referred to the Met by the Electoral Commission."
A Liberal Democrat spokesperson said the party has "always endeavoured" to ensure its reports of campaign expensive are completed in full, in good time and according to all applicable rules
"These mistakes, caused by issues with a small number of local accounting units, were a result of human error and failures of process," the spokesperson added. "We are taking steps to ensure these mistakes are not repeated in future. We will co-operate fully with any investigation."