The Prime Minister Theresa May's chief of staff has been drawn into the controversy over the Conservatives' general election expenses, currently under investigation by the police.
Channel 4 News said it had obtained evidence suggesting Nick Timothy was among a "crack team" of Tories put up by the party in the Kent seat of South Thanet where they were fighting to stop Ukip leader Nigel Farage winning a Commons seat in last year's election.
Kent Police and the Electoral Commission are currently investigating whether the Conservatives broke the law by failing to declare tens of thousands of pounds of hotel bills - including at the Royal Harbour Hotel in Ramsgate where, according to Channel 4 News, Mr Timothy stayed.
The party maintains that it acted "entirely within the law".
Under election law, expenses for the "promotion" of a candidate in a constituency must be declared locally and are subjected to tight limits.
Channel 4 News, which has previously carried a series of reports concerning the Conservatives' election expenses, said none of the expenses incurred at the Royal Harbour Hotel were declared as local expenses by the winning Tory candidate, Craig Mackinlay, or his agent.
The programme said a Conservative spokesman had confirmed to them that Mr Timothy - who was previously a special adviser to Theresa May when she was home secretary - was based in South Thanet and had "assisted" the team, but said he was working as a "volunteer" on the "national" campaign.
It said it had been told by the party that Mr Timothy's duties during the campaign included "briefing policy and political work on Home Office policy, briefing party spokespeople on Home Office policy, supporting Theresa May, and working on a variety of other matters for the Conservative Party during the campaign".
In relation to the South Thanet investigation, Kent Police said in a statement: "The Kent Police investigation into this complex matter is ongoing and officers continue to follow lines of inquiry. Therefore it would not be appropriate to comment further.
"A number of police officers continue to work on this investigation. Officers from Kent Police continue to work with the Electoral Commission as the investigation continues.
"Kent Police will not give details of live investigations or confirm lines of inquiry. To speculate on a live investigation is unhelpful and could have a detrimental impact on the outcome of the inquiry."
A Conservative Party spokesman said: "We continue to co-operate with the Electoral Commission's investigation. The Conservative Party has always acted entirely in accordance with the law."
A spokesman for Mr Mackinlay told Channel 4 News: "Our understanding is that there continues to be an ongoing investigation into the matters raised by the ITN report by both Kent Police and the Electoral Commission.
"As such it is inappropriate to comment at this time. We maintain that the South Thanet general election return was both lawful and proper."