In parliament a three line whip is said to be applied when a
party seeks to ensure every MP turns up and votes the party
line. But why the term "three line" whip? And is there such a
thing as a one or two line whip? There are indeed one and two
line whips - they basically boil down to how strong the
expectation to vote is. A single whip is simply a guideline,
while a double whip (or two line whip) is stricter - and
attendance at the vote is required. The three-line whip is a
'vote with the party or get out'. The number of lines comes from
the number of times that a vote is underlined by the Chief Whip
in the parliament's schedule.