Nigel Farage’s income since he was elected as an MP has now reached £2m on top of his parliamentary salary, analysis of the register of MPs has shown.

Farage’s earning power sets him alongside a small number of MPs who have been able to leverage their status for external income alongside their day jobs – drawing comparisons to Boris Johnson, who made about £5m on top of his MP’s salary in the six months after he resigned as prime minister.

Analysis by the investigations website DeSmog shows Farage has registered more than £2m in financial interests since July 2024, when he was elected as the MP for Clacton.

The figures come amid growing scrutiny of Farage’s wealth after the Guardian revealed last week that the Reform UK leader received and did not declare a £5m gift from his party’s mega-donor Christopher Harborne prior to the 2024 general election, potentially in violation of parliamentary rules.

Farage has said he had no need to declare the money as it was “an unconditional, non-political, personal gift”. He said he used it to pay for his security.

However, Labour and the Conservatives have criticised the non-disclosure – and on Wednesday, a senior Reform member admitted it was frustrating their leader had not declared the gift.

“There’s no question that Nigel is a rock star. And he has undoubtedly faced threats to his security. But we do need to make greater progress away from personality towards policy [as a party]. I do wonder if this could have best been avoided by declaring it in the first place. It is a disappointing distraction,” the senior party member said, speaking on condition of anonymity.

One poll published by the New Statesman on Wednesday suggested the disclosure of the gift is causing alarm among voters.

A Survation poll for 38 Degrees, a progressive campaign group, said more than two-thirds of the British public (68%) had concerns the gift could give Harborne “inappropriate influence” over Farage’s political decisions and priorities.

MPs and candidates for Reform were given “lines to take” in media interviews when asked about the gift. These included placing emphasis on the security threats Farage has faced and that the gift was unconditional and personal. On that basis, it was not necessary to declare it on the register of members’ interests, the open record of the gifts, benefits and donations MPs receive, according to the party’s briefing.

The news of the £5m gift has also created an atmosphere of disquiet within Reform HQ, according to two staffers who asked not to be named.

One summed it up as a “paranoid vibe” with constant fears about a high-level mole after the news report. The insiders also described individuals being questioned about how the Guardian discovered the £5m gift to Farage. People were “pulled aside for interrogation”, the second staffer said.

The Electoral Commission is looking into a complaint from the Conservative party about the money. Reform UK said it was given as an “unconditional gift” to Farage, who was then the party’s honorary president and had not publicly committed to standing for parliament. He had used the funds for security arrangements, the party said.

Parliamentary rules state that any benefits within 12 months before taking office should be declared, depending on whether they are for political or personal purposes. The rules state: “If there is any doubt, the benefit should be registered.”

Farage has doubled down on his assertions that there was no need for him to declare the gift.

Farage said on Tuesday that the money was “purely private” and “wasn’t political in any sense at all”. He added: “And believe you me, we’ve looked at this from every legal angle, there is no obligation to declare something that is an unconditional, non-political, personal gift. And it will ensure I can be safe for the rest of my life.”

The MP’s principal employer outside parliament has been the rightwing broadcaster GB News, which has now paid Farage £700,000 since July 2024. He registered another £40,662 from the outlet last week. He also listed a new gift from the South African businessman Avi Lasarow, who gave the Reform leader three tickets to a boxing match on 4 April worth £1,749.

“That Farage has amassed £2m from personal earnings and gifts while a sitting member of parliament should concern anyone who thinks an MP’s job is to represent their constituents,” said Kamila Kingstone, a senior campaign lead at Spotlight on Corruption.

“It’s a systemic issue and highlights a wider failure of the rules that are supposed to ensure integrity in public life. It risks blurring the lines between public service and private interests, creating the perception that some politicians are in it for themselves.”

Reform has been contacted for comment.