I can't find the term 'substantial' in the linked source. So I think maybe you are editorialising.

Here is the actual text from 4.7.

> We have investigated the allegation that Cambridge Analytica provided data analytics services to Leave.EU. Our focus has been on the use of personal data and whether Leave.EU breached the DPA98. We served Information Notices on Leave.EU and Cambridge Analytica to gather evidence as part of our investigation.

> Information placed in the public domain by some of those subject to investigation suggested a relationship between Cambridge Analytica and Leave.EU, and both sides have acknowledged there was an initial exploration of how to work together during the Referendum campaign. Brittany Kaiser, Director of Program Development at Cambridge Analytica, appeared at a Leave.EU news conference in 2015. Statements by representatives of Leave.EU made in 2016 also indicated that Cambridge Analytica had worked for them. Senior Cambridge Analytica staff also claimed they worked with Leave.EU.

> In response to Information Notices served on them, both parties have stated that only preliminary discussions took place, and the relationship did not move forward when Leave.EU failed to attain the designation as the official Leave campaign. In evidence provided to the ICO, Leave.EU stated that four meetings took place:

> 23 October 2015 representatives of Leave EU met with CA staff, this was a basic introductory meeting to express interest in potentially working together

> 18 November 2015 CA appeared at a press conference with Leave.eu

> 20 November 2015 CA went to Leave.EU’s Bristol offices and pitched their product.

> 8 January 2016 representatives of Leave.EU met CA in London, and CA presented a proposal for future work together.

The ICO report does not specify that any work was carried out, or what exactly that work was.

Also worth noting that the pdf in interim report The related findings of the final report after 3 year investigation are summerised here

https://cy.ico.org.uk/media2/migrated/2618383/20201002_ico-o...

> From my review of the materials recovered by the investigation I have found no further evidence to change my earlier view that SCL/CA were not involved in the EU referendum campaign in the UK - beyond some initial enquiries made by SCL/CA in relation to UKIP data in the early stages of the referendum process. This strand of work does not appear to have then been taken forward by SCL/CA.