The pro-Brexit campaigner Arron Banks’ former business partner has told South African police he was the middleman on cash payments between a Lesotho minister’s daughter and the British billionaire.

It follows the admission by Banks earlier this week that he paid money to a minister in the government of Lesotho just weeks before the landlocked country reportedly granted him a diamond mining licence, although he denied it was a bribe. He described the latest allegations as ludicrous.

“I thought nothing of these payments until I was asked to pay an amount in excess of R500,000 [£29,000],” Chris Kimber told police, according to a transcript obtained by Channel 4 News.

Although Banks had described the mine as a “significant find”, Lesotho’s mining commissioner, along with mineworkers, disputed the claims and said they had not seen any diamonds in the mine, which is now closing.

In further claims made to police, Kimber said: “It was decided by Arron Banks that diamonds would be acquired from third parties for export … I was later to find out that Arron Banks … was involved in illicit diamond buying in various African countries.”

Kimber reportedly told police that diamonds were not the only ambition that Banks had in Lesotho.

He alleged that Banks had a “grand plan to somehow gain a foothold whereby he would be able to not only control diamond flow, but also other aspects of the economy”.

Channel 4 News cited documents which, it claimed, suggested that Banks had tried to do business in Russia by attempting to raise funds from Alrosa, the Russian state-owned diamond company.

Documents handed to South African police accuse Banks and his partners of planning to set up a military training camp and “mercenary support” – “if need be” – to help get a friendly politician into power.

“Arron Banks was in discussion with Alrosa, the Russian state diamond producer and he had made certain promises to them. The most important was that Arron Banks was to prove to Alrosa the quality of diamonds produced”, according to the statement submitted to South African police’s investigative unit by Kimber in November 2017.

It said: “He was further due to meet representatives, in London, in November, where he would be obliged to show them the quality of the production.”

South African police in Pretoria have been investigating the claims.

In a statement to Channel 4 News, Banks said all of the allegations against him were “ludicrous” and that he had “genuine concerns about the sanity and mental health of the editorial team responsible for the reports”.