Culture secretary considers intervention to address concerns about editorial independence.

The government has dealt a blow to the Daily Mirror publisher’s £200m takeover of the Express and Star titles by signalling its intent to launch an investigation into the deal over issues including editorial independence.

The culture secretary, Matt Hancock, said on Monday he was “minded to” issue a public interest intervention notice for an in-depth inquiry and would come to a final decision “shortly”. The move follows the decision by the Competition and Markets Authority (CMA) this month to open an initial investigation into the deal.

Hancock said: “The first public interest ground is the need for free expression of opinion, and concerns the potential impact the transfer of newspapers would have on editorial decision making.”

The minister said he was also considering whether the deal raised potential completion concerns. “The second ground is the need for a sufficient plurality of views in newspapers, to the extent that it is reasonable or practicable,” said Hancock. “The merged entity would own the largest share of national titles within the UK newspaper market, owning nine out of 20 national newspaper titles.”

In February, Trinity Mirror’s shareholders voted to approve the deal to buy the Daily Express, Sunday Express, Daily Star and Daily Star Sunday newspapers, as well as magazines including celebrity title OK!. They will join its national titles the Daily Mirror, Sunday Mirror and Sunday People. However, the CMA issued an order forcing Trinity Mirror to leave Express Newspapers as a standalone business until plurality and competition concerns can be fully investigated.

Hancock and the CMA, which will decide on whether to launch a full investigation by 7 June, have the powers to block or amend the deal. If Hancock orders an investigation into the impact on media plurality, it will be carried out by the media regulator, Ofcom.

Days after the shareholder vote, the editors of the Daily Express and Daily Star resigned. Trinity Mirror immediately announced the appointment of two of its own executives – the Sunday Mirror and Sunday People editor, Gary Jones, and the Daily Mirror associate editor, Jon Clark – as replacements.

Simon Fox, the Trinity Mirror chief executive, has repeatedly pledged that his Labour-supporting Daily and Sunday Mirror will keep Desmond’s Brexit-supporting titles editorially independent.

Reacting to the announcement of an investigation he said: “This is a part of the process that we were aware was possible following our acquisition of the Northern & Shell publishing assets. We continue to believe there are no plurality or competition issues.

“We would expect any review by Ofcom arising from this DCMS statement would happen in parallel with the CMA review, which we expect to conclude by June 7 2018.”