The Liberal Democrats have been the £20,000 by the election watchdog for failing to properly report its 2015 general elections pending.

The fine is the maximum amount which the Electoral Commission could impose on the party.

An investigation by the watchdog found the Lib Dems had failed to declare 307 separate payments totalling £184,676 in their returns.

The commission also found more than half of the missing payments did not have any invoices.

The party lost 49 seats in the election, their worst result.

The body has informed the Metropolitan Police of a possible criminal offence by the party's registered campaigns officer, Tim Gordon, under Section 83 (3) of the Political Parties, Elections and Referendums Act 2000.

The law states party treasurers must examine the returns to the "best of his knowledge and belief" and they are complete and correct.

A written submission declaring the submission to be complete was handed to the watchdog by Mr Gordon.

In its report into the missing payments, the watchdog states "some persons within the party were aware of some of the missing payments before the spending return was submitted".

The commission's director of political finance and regulation and legal counsel said: "Our investigation uncovered systemic failures in ensuring that the rules were being followed.

"The party and its officers cooperated 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."

He added: "This also highlights why we have been calling on the UK Government to make higher sanctioning powers available to us.

"With millions of pounds being spent by large parties looking to form national governments, a fine of £20,000 is no longer a strong enough deterrent to ensure the rules are properly followed."

A Liberal Democrat spokesman said: "We always endeavour to ensure our reports of national campaign expenses 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.

"We are taking steps to ensure these mistakes are not repeated in future. We will co-operate fully with any investigation."

In October, Labour was also fined £20,000 by the Commission for failing to declare all of its general election expenses.