A senior Conservative campaigner has denied breaching strict election spending limits to help defeat Nigel Farage in the key South Thanet general election seat in 2015, a court has heard.

Marion Little, 63, was said to have effectively run the campaign for the local Tory candidate, Craig Mackinlay, who eventually won, fighting off the challenge from Farage, then the leader of Ukip.

Little, who began working for the party in 1974, said while the seat was considered important for the Tories to win, she did not create or falsify documents.

Giving evidence from the witness box for the first time in the trial at Southwark crown court, which began on 16 October, Little said the South Thanet seat had been top of the list of Conservative priorities.

“It was a very important seat because of all the media Mr Farage had gathered,” she said.

Asked by the defence counsel, Jim Sturman QC, whether it was considered “so important” that she falsified documents relating to campaign expenses, Little replied: “I would never do anything like that. I have never falsified or knowingly done anything like that.”

Little, of Ware, Hertfordshire, denies three counts of intentionally encouraging or assisting an offence under the Serious Crime Act 2007.

Mackinlay, from Ramsgate, Kent, denies two charges of making a false election expenses declaration under the Representation of the People Act 1983.

A third defendant, the 29-year-old Tory aide Nathan Gray, of Hawkhurst, Kent, denies a similar charge.

Prosecutors previously suggested to jurors that Mackinlay, 52, Gray and Little deliberately submitted “woefully inaccurate” expenditure returns.

Declared spending on the campaign came in under the strict £52,000 limit set for the MP’s South Thanet constituency. Prosecutors allege up to £66,600 of additional expenditure went on staffing, accommodation, advertising and other costs for Mackinlay’s campaign that was not declared.

Their trial previously heard that the Conservative party put extra resources into the campaign to win the seat in Kent on 7 May.

The prosecutor, Aftab Jafferjee QC, told jurors it became a “two-horse race”, which was won by Mackinlay with a majority of about 2,800 in an electorate of 70,000.

“In those pre-referendum days, Ukip were on the rise and the threat perceived by the Conservative party to their share of the vote only intensified in the lead-up to the 2015 election,” he said.

“When Nigel Farage announced that he would step down as leader of Ukip if he failed to win the South Thanet seat, it was clear that this was not going to be any ordinary election campaign,” he added.

Giving evidence on Monday, Little described how “all the hoardings” in South Thanet in the run-up to the election appeared to have a Ukip poster on them, often featuring Farage’s face.

The trial, which is expected to last until December, continues.