Cambridge Analytica did work for Leave.EU on the EU referendum, according to emails published by a House of Commons committee, even though the company never received payment for it.

Brittany Kaiser, the former director of business development at the shuttered political consultancy, supplied the emails to the digital, culture, media and sport committee. She argued that they showed that, despite claims to the contrary, the partnership between the two organisations went beyond exploring the potential for future collaboration.

“Chargeable work was completed for Ukip and Leave.EU, and I have strong reasons to believe that those data sets and analysed data processed by Cambridge Analytica … were later used by the Leave.EU campaign without Cambridge Analytica’s further assistance,” Kaiser wrote in a letter to Damian Collins, the committee chair.

The emails show Cambridge Analytica staff, including Julian Wheatland, the company’s chief operating officer, discussing with Leave.EU staff whether or not to share the results of analysis performed on Ukip data. “We have generated some interesting findings that we can share in the presentation, but we are certain to be asked where the data came from. Can we declare that we have analysed Ukip membership and survey data,” Wheatland asked Leave.EU’s Andy Wigmore and Ukip’s then general secretary, Matthew Richardson. He was rebuffed.

Wheatland also told Cambridge Analytica staff that the relationship was intended to be formalised. “I had a call with Andy Wigmore today (Arron [Banks, founder of Leave.EU]’s right-hand man) and he confirmed that, even though we haven’t got the contract with the Leave written up, it’s all under control and it will happen just as soon as Matthew Richardson has finished working out the correct contract structure between Ukip, CA and Leave,” Wheatland said in an email to Cambridge Analytica staff.

In fact, Cambridge Analytica was never paid for the work it carried out. In her letter to Collins, Kaiser said: “Despite having no signed contract, the invoice was still paid, not to Cambridge Analytica but instead paid by Arron Banks to Ukip directly. This payment was then not passed on to Cambridge Analytica for the work completed, as an internal decision in Ukip, as their party was not the beneficiary of the work, but Leave.EU was.”

A Ukip spokesman disputed that any money paid by Banks to Ukip was intended to be passed on to Cambridge Analytica, and said Kaiser’s allegations against the party had already been investigated by the Information Commissioner’s Office in 2018. “We took the data to Cambridge Analytica, who looked at the data, and then we took the data away,” the spokesman said. “We refused the service, frankly because it was too expensive, and we didn’t want to engage with what they were doing.”

Cambridge Analytica and Leave.EU have long maintained that the analysis was only carried out for the purposes of pitching for a more permanent arrangement. Richard Tice, a co-founder of Leave.EU, said in 2018 that Cambridge Analytica “received no data or undertook any modelling for Leave.EU”.

At the time, 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.”

In response to the release, the DCMS committee member Ian Lucas called on the Electoral Commission to reopen its investigation into Leave.EU “in view of the additional evidence from Brittany Kaiser”.

Collins said: “There are important questions to follow up, in particular whether the data sets created by Cambridge Analytica were used in the referendum or other campaigns and if they were, whether or not it was a breach of data protection law for Ukip voter data to be used in this way – that certainly seems to be something that they themselves were concerned about.”