He argued that any business discussions that emerged from those meetings were insignificant because he had never “done any Russian deals,” so “after the wholesale theft of my emails, there is still no smoking gun there.”

But Damian Collins, who is chairman of the parliamentary committee investigating the potential Russian use of disinformation to influence the Brexit vote, said he had seen a record of the messages about the potential Russian mining investments and questioned Russian intentions toward Mr. Banks.

“The question is, Why would the Russians do this for Banks?” Mr. Collins asked in an interview. “What it looks like is that Russia decided he was someone they wanted to do business with and they wanted to see prosper and succeed — and Banks, alongside that, wanted to hide the extent of his contacts with the Russians.”

With no college degree, Mr. Banks first became wealthy by starting insurance companies that sold policies to motorcycle riders and van drivers. He now owns a complicated network of insurance and finance enterprises as well as a few diamond mines in South Africa, where his father operated sugar plantations.

He first rose in prominence in Britain through his role in the campaign to leave the European Union, and he has published a campaign memoir, “The Bad Boys of Brexit.”

Some of his emails were first leaked earlier this month to the British press. But the broader record of his messages, described this week to The New York Times by several people who had read them, revealed the new disclosures about Mr. Banks’s more extensive Russian business dealings.

In the Friday interview, Mr. Banks eventually admitted to a fourth meeting with the Russian ambassador, though he described the earlier account he gave to Parliament of two lunches and a cup of tea as “relatively accurate.”