Farage is already under investigation by the standards watchdog over whether he should have declared a STG5 million ($A9.7 million) donation from a cryptocurrency billionaire he received before entering parliament.
The Sunday Times reported Farage was provided with security services, social media support and accommodation by George Cottrell, a long-standing ally, in the year before Farage was elected an MP in 2024.
Farage's spokesperson said the story was "baseless and contrived".
"No parliamentary rules have been broken," he said.
But Josh Babarinde, a lawmaker in Britain's Liberal Democrats party, wrote to the Parliamentary Commissioner for Standards on Sunday, calling for an investigation into the new allegations.
"Given the value and nature of the support described, there is a serious question as to whether Mr Farage met his obligations under the Code of Conduct for MPs," he said in a letter he made public on X.
"This is not an isolated concern."
The right-wing, anti-immigration Reform UK party tops national opinion polls, making Farage a possible future prime minister after a 2029 election and raising scrutiny of the party and its leader's finances.
According to the Sunday Times, Cottrell went to prison in the US in 2017 after pleading guilty to wire fraud and now works in cryptocurrency.
Under parliamentary rules, new MPs must declare financial interests and "registrable benefits" received in the previous 12 months, although personal gifts are exempt.
"I think quite a lot of questions come up in relation to his (Farage's) finances. He seems to have a bit of a flexible relationship with transparency," Britain's Health Minister James Murray told the BBC on Sunday.
Farage has said the STG5 million he received from Thailand-based crypto investor Christopher Harborne before he announced he would stand as an MP in 2024 was an unconditional gift and exempt from disclosure rules.
He has also said the money was intended to fund his personal security.
The donation was not publicly disclosed until reported by a newspaper in April.
Farage is awaiting the outcome of the investigation.
If he is found to have committed a serious breach of parliamentary disclosure rules, he could be suspended from the House of Commons.
A suspension of 10 days or more could trigger a recall petition, potentially forcing a by-election in his constituency.
