The proposed deal, announced in February, would see Nielsen acquire Ebiquity’s advertising intelligence arm, which provides data linking advertising creative with spend and allows clients to analyse competitor advertising.

Today ( 13 June) marks the end of the CMA’s initial assessment on whether the deal would result in lessening of competition. The regulator said in a statement: "While they face some competition from firms offering this service for digital advertising, no firm competes with Nielsen and Ebiquity for detailed intelligence across all UK media channels."

The CMA added that this also applies for the supply of intelligence on international advertising to UK customers.

Competition may be "significantly reduced" if the merger went ahead as planned, the statement said.

Nielsen and Ebiquity have been issued a deadline of 20 June to offer a solution. If concerns are not met, the regulator will conduct a more in-depth, ‘phase two’ investigation.

Ebiquity said in a statement: "Ebiquity and Nielsen now have the opportunity to offer remedies to address the CMA’s concerns. If appropriate remedies are not offered or agreed, the transaction will be referred for a Phase 2 investigation. Ebiquity and Nielsen continue to believe that the transaction will deliver substantial benefits for all stakeholders."

A Nielsen spokesperson said: "Nielsen acknowledges the Competition and Markets Authority (CMA) announcement and will follow procedures to address any questions and concerns, as well as timelines and next steps."