The Electoral Commission has launched an inquiry into whether the Conservatives violated election spending rules at the general election.
An investigation by Channel 4 News said that alleged irregularities in recording expenses in Thanet South meant the Tories broke spending limits during the campaign.
During last year's election Ukip’s Nigel Farage lost to the Tories’ Craig Mackinlay in one of the most high-profile contests in the country.
The loss for Ukip sparked Mr Farage’s short-lived resignation as party leader.
However, the Conservatives were said to have attributed £14,000 worth of hotel bills spent for activists in Thanet South to “national” election expenditure rather than to Thanet South’s account.
Parties were restricted to spending a maximum of £15,016 on the constituency – allocating the bills to national expenditure may have meant the Conservatives were able to spend more money on other campaigning activity to win the crucial vote.
The amount of money allowed to be spent in any given seat at the general election per party is £8,700, plus six pence for every person on the electoral register.
The strict rules are in place to make it more difficult to swing a seat simply by spending large amounts of money on professional campaigning.
General election 2015: Polling day
General election 2015: Polling day
1/16 General election 2015
Nuns arrive to vote at a polling station at St John's Church in Paddington, London
2/16 General election 2015
A voter leaves the White Horse Inn in Priors Dean, also known as the 'Pub with no name', which is part of the East Hampshire constituency and acts as a local polling station on the day of the election
3/16 General election 2015
General view of inside the White Horse Inn in Priors Dean
4/16 General election 2015
People cast their votes as a man uses a punch bag in the East Hull Boxing Academy, which is being used as a polling station in Hull
5/16 General election 2015
Penny Higbee waits to greet voters at her home in Routh, East Yorkshire, which is being used as a rural polling station
6/16 General election 2015
Voters in Ironbridge, Shropshire, arrive to cast their vote at The Iron Bridge Tollhouse
7/16 General election 2015
A voter arrives at the North West Ambulance Service Station at Milton Green, Cheshire, which is being used as a polling station as Britain goes to the ballot box
8/16 General election 2015
A polling station has been installed in a launderette in Oxford
9/16 General election 2015
SNP candidate for the Gordon constituency and Former First Minister Alex Salmond with first time voter Nicki Falconer, and her family, (L-R) Mackenzie, Nicki, Skye, Alex Salmond and Keiran at their local polling station in the Gordon constituency in Ellon, Scotland
10/16 General election 2015
Prime Minister David Cameron and wife Samantha after casting their votes at Spelsbury Memorial Hall, Witney
11/16 General election 2015
Liberal Democrat leader and Deputy Prime Minister Nick Clegg and his wife Miriam Gonzalez Durantez arrive at Hall Park Hill Community Centre to cast their votes, in Sheffield
12/16 General election 2015
Labour Party leader Ed Miliband and his wife Justine Thornton leave the polling station at Sutton Village Hall in Sutton after casting their votes in the 2015 general election in Doncaster
13/16 General election 2015
First Minister of Scotland and leader of the SNP Nicola Sturgeon, votes with her husband Peter Murrell in Glasgow, Scotland
14/16 General election 2015
Ukip leader Nigel Farage arrives to cast his vote for the South Thanet constituency in Ramsgate
15/16 General election 2015
Plaid Cymru leader Leanne Wood arrives at a polling station in Penygraig, Rhondda, Wales
16/16 General election 2015
Green Party leader Natalie Bennett after casting her vote at Ossulston Tenants' Hall, London
Kent Police said yesterday it had shelved an investigation into claims the party’s local election agent broke the law by failing to fully disclose election expenses.
Today the Electoral Commission, which regulates elections, says it has started its own probe in light of the police dropping theirs.
“The priority of the Electoral Commission is to conduct a fair and thorough investigation and the time taken to complete an investigation varies on a case-by-case basis,” the Commission said in a statement.
“Once the investigation is complete, the Commission will be able to decide whether any breaches have occurred and if so what further action, if any, may be appropriate.
“The Commission’s sanctioning powers are limited to a civil penalty of up to £20,000.”
A spokesperson for Kent Police said further police involvement in the episode had not been ruled out.