Another report, published in 2016 during the run up to the Labour leadership election, analysed 465 online news items from 8 providers and 40 prime time television news bulletins on BBC One and ITV over a 10-day period .
It reported a "clear and consistent bias in favour of critics of Jeremy Corbyn".
Despite strict broadcast impartiality rules, the report confirmed that on the mainstream news bulletins, there was twice as much time on air awarded to voices critical of Corbyn than those in support.
The evening news also showed a tendency towards negative and even insulting language when describing Corbyn and his supporters, the word 'hostile' was highlighted in the report.
Online news sites were also found to be comparatively biased.
In all but one of the online news outlets, across both the left and right-wing political spectrum, there were more views opposed to Corbyn than in favour.
Dr Justin Schlosberg, author of the report and chairman of Media Reform Coalition, said:
This research shows that bias in mainstream media coverage of the Labour Party crisis was not inevitable or unavoidable given a minority of outlets that were relatively balanced.
Amidst the social fracturing and polarisation of democratic life post-Brexit, the need for a more plural and inclusive mainstream news media has never been more urgent.
We hope that broadcasters and editors will respond positively to our call to consider the impact of imbalanced reporting on the democratic process.
But did they?
The Independent, the Huffington Post and the International Business Times were among the online outlets found to have had the least biased coverage of Corbyn.
But while The Independent and Huffington Post “exhibited a slight tendency to favour sources critical of the Labour leadership and the issues they tended to highlight,” the IBTimes was the only outlet to have given “relatively greater prominence” to Corbyn’s supporters and issues they raised.
In September 2016, polling organisation YouGov found that 51 per cent of British adults agreed that media coverage of Corbyn had been "deliberately biased," while 29 per cent disagreed.
The Independent's Jon Stone reported at the time that Labour voters were even more adamant, with 69 per cent alleging bias.
But will it change in time for the general election?
Media Reform's blog post, 'Five myths about Corbyn media bias', makes the point that while almost two years of consistent negativity have done little to dent his support among grassroots Labour voters, the overall effect on the national voting mindset is another story.
It is true that the overwhelming editorial attacks on Corbyn since he was first put on the Labour leadership ballot seems to have done little to dent his support.
But his critics rightly point to a different story told by national polls which suggest that beyond the grassroots, Corbyn carries little favour with the electorate at large.
Indeed, editors have tended to justify their particular news judgements about Corbyn on the basis of these poll ratings.
But this assumes that the polls influence the news agenda rather than the other way around.