Richard Bridge wrote: "The Mail would shoot anyone who read a red-top. It's a blue top. In the UK blue=conservative=capitalist=right-wing, red=labour (or preferably old-labour)= socialist (not a term of abuse here)=left-wing".

The term "red top" isn't really a politically-motivated term, but one describing a particular type of tabloid and refers more to the literal colour of the masthead than where the journalism appears on a political compass. The other colour distinction, which didn't really catch on, was the 'black top'.

The Sun - classic red top material - often has very right of centre journalism and is a reactionary as the above mentioned Daily Hate Mail. In fact, journalists have made the move from one paper to the other. I don't think The Sun has been an blatantly (old) Labour paper since the mid-1970s.