The director of Vote Leave has denied allegations of links between his campaign and Cambridge Analytica.
Dominic Cummings said claims by the Observer newspaper are "factually wrong, hopelessly confused, or nonsensical".
Cambridge Analytica is facing claims it amassed the data of millions of people without their consent.
The Observer is expected to publish further claims about links between the official Brexit campaign and the firm.
Cambridge Analytica is at the centre of a row over whether it used the personal data of millions of Facebook users to sway the outcome of the US 2016 presidential election and the UK Brexit referendum.
Mr Cummings claimed stories alleging links with Vote Leave were being promoted because a "powerful set of people will do anything to try to shift public opinion in order that they can overturn the referendum".
He says testimonies he expects to be made public in the coming days were from "whistleblowers" who were "peripheral, making invented claims about things they didn't see".
Mr Cummings has also published emails that appear to suggest Chris Wylie, who has been at the centre of the allegations about Cambridge Analytica, tried to sell Vote Leave a similar service, but was turned down.
Mr Wylie's lawyers have been contacted for a response.
The blog also rejects any suggestions that Vote Leave was in any way linked to Cambridge Analytica.
Vote Leave spent £2.7m on the services of a Canadian digital agency Aggregate AIQ in the run-up to the June 2016 EU referendum.
In his blog, Mr Cummings says AIQ "once built some software" for Cambridge Analytica's parent company SCL, in 2014, but suggestions the company shared data with Cambridge Analytica were "ludicrous".
In a separate development, Brittany Kaiser, Cambridge Analytica's former business development director, has told the Guardian the firm carried out data analysis for Leave.EU, the rival Brexit campaign to Vote Leave that was fronted by Nigel Farage.
Cambridge Analytica has said it did "no paid or unpaid work" for Leave.EU.
Ms Kaiser claims in The Guardian some work was undertaken, although no payment was received.
Leave.EU's co-founder Arron Banks said: "Leave.EU did not receive any data or work from Cambridge Analytica.
"UKIP did give Cambridge Analytica some of its data and Cambridge Analytica did some analysis of this.
"But it was not used in the Brexit campaign. Cambridge Analytica tried to make me pay for that work but I refused. It had nothing to do with us."
Cambridge Analytica has suspended its CEO, Alexander Nix, who was filmed as part of a Channel 4 investigation giving examples of how the firm could swing elections around the world with underhand tactics such as smear campaigns and honey traps.
The company has offered to hand over all communications between its elections arm, SCL Elections Ltd, and a firm run by academic Dr Aleksandr Kogan by 5pm on Monday to the Information Commissioner, the High Court heard.
Lawyers representing the Information Commissioner's Office, which is investigating allegations against the firm, said its offer was "a poor second best" and are pursuing their application for a warrant.
Both Cambridge Analytica and Facebook deny any wrongdoing. The hearing before Judge Leonard continues.
A group of campaigning lawyers have, meanwhile, won the first stage of their High Court challenge over election spending in the run-up to the EU referendum.
The Good Law Project (GLP) says the Electoral Commission failed in its duty to regulate the referendum process in relation to spending by the Vote Leave campaign ahead of the vote in 2016.