The Conservative Party has been fined a record £70,000 and its former treasurer reported to the police following a report by the Electoral Commission into its election expenses.

The investigation – launched after a series of reports by Channel 4 News over the past year – found “significant failures by the party” to report spending in the 2015 General Election and in three by-elections in 2014.

The Commission also suggested that the advantage gained by the party via spending that was incorrectly recorded “meant that there was a realistic prospect that this enabled its candidates to gain a financial advantage over opponents”.

It comes just two days after a dozen police forces separately passed files to the Crown Prosecution Service over allegations that up to 20 Conservative MPs breached election laws.

Channel 4 News yesterday broadcast new secret emails – which reveal how two more of Theresa May’s closest advisors were involved in the most controversial campaign of all – the party’s battle against Ukip leader Nigel Farage in South Thanet.

The investigation by the Electoral Commission found the Conservative Party’s national spending return for the 2015 General Election was missing at least £104,765 of payments, while a further £118,124 of payments were either incorrectly reported or not reported at all.

The election watchdog has referred former Conservative Party Treasurer and Chief Executive of the Conservative Party Simon Day to the Metropolitan Police on suspicion of “Knowingly or recklessly making a false declaration would be an offence” under legislation.

Read the full timeline of the Election Expenses investigation - every report, the documents and profiles of all the key characters.

Election laws exist to preserve fairness in the democratic process and ensure a level playing field.

Political campaigning is an increasingly sophisticated business, and a political party with more money has the potential to reach – and persuade – a greater number of people.

Under election laws, both political parties, and their candidates, must declare all their campaign spending, and stick within strict spending limits that prevent richer parties gaining an unfair advantage.

‘Hindered and caused delay’

In a statement the Conservative Party said it “had complied fully with the Electoral Commission’s investigation since it began more than a year ago.”

However, the Electoral Commission’s report said the party had repeatedly failed to cooperate, causing delays to the report.

The report also states: “While at times answers were forthcoming, and in particular cooperation was given when arranging interviews with certain Party officials, at other times the Party hindered and caused delay to the investigation.”

Numerous failures

Sir John Holmes, Chair of the Electoral Commission said: “Our investigation uncovered numerous failures by a large, well-resourced and experienced Party to ensure that accurate records of spending were maintained and that all of the Party’s spending was reported correctly.”

A Conservative spokesperson said: “CCHQ accepted in March 2016 that it had made an administrative error by not declaring a small amount constituting 0.6 per cent of our national spending in the 2015 election campaign.

“This error was subsequently corrected and the Party has since improved its accounting practices, reporting structures and staff guidance.

“Even taking this into account, the Conservative Party still considerably underspent the statutory national spending limits for the 2015 general election.

“Political parties of all colours have made reporting mistakes from time to time. The Labour Party and Liberal Democrats both failed to declare sums of money which constituted a larger proportion of their national expenditure in the 2015 general election.”

Background to the investigation

The year-long investigation by the Electoral Commission began after Channel 4 News unearthed compelling evidence that the Conservative Party may have abused election laws to fight three by-elections in 2014 and win power in the 2015 General Election.

More than a dozen police investigations looking into 27 sitting Conservative MPs were also launched.

Downing Street is reportedly “deeply worried” by the probes with senior figures fearing up to half a dozen constituency votes could be declared void resulting in a string of by-elections.

If you have any information - here is how you can contact the Channel 4 News Investigations team.

Kent Police investigation

Just last month Channel 4 News revealed a cache of secret documents showing the Prime Minister’s chief of staff Nick Timothy apparently played a central role in one of the campaigns under investigation, South Thanet, where Craig Mackinlay MP defeated then-UKIP leader Nigel Farage.

The emails between Conservative campaigners could be crucial to the probe by Kent Police which is examining whether a group of Conservatives who stayed at the Royal Harbour Hotel during the campaign, including Mr Timothy, worked on the Mackinlay campaign.

Channel 4 News has previously revealed that the £14,000 bill at the hotel was declared on national rather than local expenses, however, if any of the Conservatives staying there worked to promote the candidate, then this cost, or part of it, should have been declared on local spending returns.

Emails seen by this programme appear to show Mr Timothy devising strategy and campaigning messages that were used by Mr Mackinlay’s local campaign. However, the Conservative Party said Mr Timothy was a volunteer assisting the Conservative Party’s national campaign.

There is no suggestion that Mr Timothy was responsible for declaring campaign spending in the seat. A spokesman for Craig Mackinlay said: “We maintain that the South Thanet general election return was both lawful and proper.”

Battlebus

The police investigations are also looking into the Conservative Party’s controversial ‘Battlebus’ campaign which used a fleet of coaches to parachute volunteer activists into 29 key marginal constituencies in the final ten days of the election campaign.

The Conservative Party insists that the Battlebus tour was a national event, with activists promoting the party, and not specific candidates, so costs did not need to be declared on local returns..

However, Channel 4 News has obtained material that appears to show the volunteers spent time campaigning for local candidates in addition to supporting the national campaign — handing out candidates’ leaflets and even reading from a script that mentions individual candidates by name.

A series of social media posts also suggest activists were supporting local campaigns.

Earlier this month, married couple Gregg and Louise Kinsell also came forward to Channel 4 News to say they campaigned for local candidates when they joined one of the Battlebus coaches in the South West which visited four constituencies in the final days of the campaign.

Under election laws, any costs incurred to promote a local candidate, must be declared on local candidate spending returns. It’s a criminal offence to knowingly make a false declaration.

However, the costs for hiring the Battlebus coaches, and wrapping them in branded livery, were declared on the Conservative Party’s national expenses. Just under £40,000 spent on hotels, uncovered by Channel 4 News, was not declared at all which The Conservative Party said was an “administrative error”.

Following the allegations made by Mr and Mrs Kinsell, a Conservative Party spokesman said: “We are cooperating with the ongoing investigations.”