Rupert Murdoch’s bid to take control of the whole of Sky through his entertainment business 21st Century Fox should be rejected on competition grounds alone, according to research to be published on Wednesday.

In a submission to the minister considering the bid, campaigners at the Media Reform Coalition and online activist network Avaaz argue that the overall market shares of both Murdoch-owned newspapers the Sun and the Times as well as Sky remain “materially unchanged” since 2011, when media regulator Ofcom raised concerns about a similar takeover.

The report, which urges the culture secretary, Karen Bradley, to reject the bid given the “unprecedented case for intervention on plurality grounds”, is to land on her desk as Fox is expected to formally notify the European competition regulator of its £11.7bn bid for full control of Sky this week.

Justin Schlosberg, the chair of the coalition, said the situation in terms of media competition was “definitely no better than last time and probably worse”.

In support, he cited the fact that the Sun’s audience reach had increased after the removal of the paywall for its digital content despite declining print circulation; the increased reach for Sky television services through digital services such as YouTube; and research from Cardiff University last year that the newspapers had a disproportionate impact on broadcasters, for example.

Cardiff University research on coverage of the 2015 general election “demonstrates the influence of national newspapers – and News UK titles in particular – over the issue agenda of broadcasters including the BBC”, it said.

Supporters of the bid by Fox, which is 39% owned by the Murdochs, have argued that an increasingly competitive media landscape with digital rivals such as Google and Facebook has diminished the influence of the family’s media empire in the UK. Fox executives have argued that there is no need even for a referral given the increased competition.

However, the coalition, which argues that the British media market place is one of the most concentrated in the world, believes media concentration has increased since 2011.

In the summary to the report, the coalition argues that its objections are “linked to, but separate from” the concerns over the “fit and proper” person test. This was raised during the last attempt by the Murdochs to take over the whole of Sky at the height of the phone-hacking scandal in 2011.

Separately, Lord Puttnam has introduced an amendment to the digital economy bill, which would subject all media takeovers to the fit and proper test and which is expected to be debated in the House of Lords.

This comes after a group of cross-party politicians including Ed Miliband has demanded that the regulator launch an immediate review of whether James Murdoch meets such a test to hold a UK broadcasting licence.

Given that James Murdoch is the chairman of Sky, Fox supporters believe there are no grounds for such a test.

The report, Consolidating Control: the Fox/News merger and news plurality in the UK, also raises concerns about the “editorial independence of Sky News, one of only two British television news channels with an average monthly audience reach of 10 million”.

The coalition argues that Sky News online is the most widely featured news source on Yahoo’s UK news page, accounting for more than 25% of articles in February 2017 and over 50% of headlines.

