Image copyright Reuters Image caption Lib Dem leader Nick Clegg resigned in 2015, after the party kept just eight of the 57 seats won in 2010

The Liberal Democrats have been fined £20,000 by the Electoral Commission for failing to declare all their spending in the 2015 general election campaign.

An investigation by the commission found that 307 payments totalling £184,676 were missing from the party's spending return.

The commission said it had referred the matter to the police to see if any criminal offences had been committed.

The Lib Dems said "human error and failures of process" were to blame.

Bob Posner, director of political finance at the Electoral Commission, said their investigation uncovered "systemic failures in ensuring that the rules were being followed".

"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," he said.

"This is why we have applied the highest financial penalty available to us."

The commission repeated its call for an increase to the maximum penalty, saying a £20,000 fine was no longer a strong enough deterrent to the larger political parties which spend millions of pounds.

The commission said it had notified the Metropolitan Police that the campaigns officer, Tim Gordon, may have committed a criminal offence if he "knowingly or recklessly signed a false declaration" about the spending.

'No repeat'

A Liberal Democrat spokesperson said the mistakes had been caused by issues with a small number of local accounting units.

He said steps were being taken to ensure these mistakes were not repeated, and the party would co-operate fully with any investigation.

"We always endeavour to ensure our reports of national campaign expenses are completed in full, in good time and according to all applicable rules," he added.

The Liberal Democrats were badly defeated in 2015, keeping just eight of the 57 seats they had won in 2010.

In October, Labour was also fined a maximum £20,000 for failing to declare all of its general election expenses, including an 8ft stone tablet, known as the "Ed Stone", that was carved with ex-leader Ed Miliband's key pledges.