As someone who only follows UK politics tangentially, this week was the first time that I heard the term Three Line Whip in the context of the Article 50 vote. Some googling gave me an idea of what is meant by it, but I still wonder why it was making headlines.
Was the Three Line Whip noteworthy because a Three Line Whip is a rare event, was it rather the polarising subject that made it stand out or a combination of both factors?
Three line whips aren't particularly common, since not all debates end with a division (votes), and the party will not have a policy on all matters. Moreover a three-line whip instructs the MP that they absolutely have to attend, excluding the possibility of dealing with other political affairs, whereas for lesser whipped options an MP might be able to "pair" with a member of an opposing party (i.e. both agree not to vote, thus freeing the MPs to conduct other business without changing the result).
Obviously three line whips are far more common for more important votes though, which obviously the "Brexit bill" counts as. Some points made the Labour party whip particularly notable in this case though were that:
The popular expectation in the media therefore had been that Labour would either offer a free vote (allowing their MPs to vote their consciences) or to whip weakly, thus avoiding the awkward disciplinary questions of what to do when individual MPs rebelled.
