The Liberal Democrats have been hit with a maximum £20,000 fine by the Electoral Commission for failing to declare hundreds of items of campaign spending at the general election.

The watchdog has notified the police of a possible electoral offence after 307 payments totalling £184,676 were found to be missing from the Liberal Democrats’ spending return “without a reasonable excuse”.

In addition, invoices supporting 122 out of the 307 payments were

missing from the return. It found the declaration to the Electoral Commission may have been signed recklessly, as there was evidence indicating some people in the party knew it was incorrect.

The Lib Dems said it was a result of “human error and failure of process”. However, Bob Posner, the director of political finance at the Electoral Commission, said there were “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.

“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.”

It comes after Labour was hit with a £20,000 fine in October for similar missing election expenses, including more than £7,000 on the “Ed Stone”.

It found two payments totalling £7,614 missing from the party’s

election return that were spent on the stone tablet on which the then

Labour leader, Ed Miliband, had carved his six key election pledges, promising to display it in the Downing Street rose garden if he won the election.

After the commission launched its investigation, the party undertook an internal review, unearthing 24 other undeclared election expenses totalling £109,777.

However, the commission’s investigation then identified 49 further

missing payments totalling £11,357 that related to the transport of

the party’s activists on the Labour Express tour and Labour Students tour during the election.

Conservative spending at the election remains under intense scrutiny after a Channel 4 investigation alleged some local spending was allocated to the national account to avoid tight limits for each constituency. About nine police forces have been investigating the accusations of higher-than-permitted spending in a number of marginal seats, which could have helped the Tories gain a majority at the election.