Nigel Farage bought a £1.4m property in cash shortly after receiving a £5m personal gift from the crypto billionaire Christopher Harborne.

The revelation came as the Reform UK leader appeared to change his line on the reason for the £5m gift, saying in an interview on Thursday that it was a “reward” for campaigning for Brexit for 27 years.

Since it was revealed last month by the Guardian, Farage had maintained that the money was given to cover his personal security.

Both developments came on a day when parliament’s standards watchdog confirmed that the MP was under a formal investigation over the gift from the Thai-based businessman.

Asked about the purchase of the property, which is outside London, a Reform UK spokesperson said: “The relevant chronology is straightforward. The offer and purchase process for the property commenced before the gift.

“Mr Farage had already passed proof of funds and the relevant checks before receiving the gift. The purchase was therefore already proceeding independently of it.”

However, Labour called on the Reform leader to state in full what the £5m was used to pay for after Sky News reported on the house purchase. Documents for it have also been seen by the Guardian.

The secluded property has been subject to several applications for extension and redevelopment, all now approved, since he bought it in 2024. It is one of four owned by Farage, whose partner owns a fifth that he uses in his constituency of Clacton.

The site itself also has several significant historical features that are likely to resonate with Farage’s own interests as a history buff.

Anna Turley, the chair of the Labour party, said: “Nigel Farage has repeatedly dodged questions on his multimillion-pound ‘gift’.

“Now we can see why – this totally stinks. Farage must urgently come clean with the public as to what this £5m was used for and why he failed to declare it.”

Hours earlier, the Reform leader’s name was published on the website of the parliamentary commissioner for standards, which states he is being investigated over an alleged “failure to declare an interest”.

The inquiry was opened on Wednesday, according to the entry, which confirms he is being investigated under rule 5 of the code of conduct for MPs.

Farage has said the gift did not need to be declared because it was intended to cover his personal security costs. However, other parties argue that the money falls within rules requiring MPs to declare any potentially relevant gifts or donations received in the 12 months before entering parliament.

Rule five of the code of conduct obliges MPs to “fulfil conscientiously” requirements relating to their registration of interests.

It states that new MPs must register all their current financial interests, and any registrable benefits (other than earnings) received in the 12 months before their election. This must be done within one month of their election, and they must register any change in those registrable interests within 28 days.

Some personal gifts are exempt from the reporting rules if they “could not reasonably be thought by others to be related to membership of the house or to the member’s parliamentary or political activities”, according to the code of conduct and rules for MPs.

The rules state: “Both the possible motive of the giver and the use to which the gift is to be put should be considered. If there is any doubt, the benefit should be registered.”

Farage is one of five MPs who are the focus of investigations by the standards watchdog, although he is the only one being investigated under rule five.

If the investigation finds Farage committed a particularly serious breach of parliamentary declaration rules, he could be suspended from the Commons. A suspension of 10 days or more could trigger a recall petition, potentially forcing him to fight again for his Clacton seat.