The report is written by a liberal institution. Contrary to the report, in my opinion the Guardian and the Daily Mirror, are not left-wing (itself a loose term). The Guardian, for example, gives voice to some left-wingers, but it is generally liberal.
The last few decades has made anyone who is not (neo)liberal, a left-winger. The dominant press of the 5 families have redefined what a left-winger is. 

Journalistic Representation of Jeremy Corbyn in the British Press