Rayner's "scum" allegation was highly relevant because the voting public do not want their politicians descending into street language and attitude (Rayner has form - she has called Tories scum in the House of Commons before now). There needs to a degree of civility among members of the various parties, because at times, politicians have to work together for the sake of the country, and it makes it impossible if the Deputy Leader of Her Majesty's Opposition, thinks and says that all members of the government are scum.
point in case. Thanks for proving my point,