original_query: What is the significance of the Parliamentary Labour Party (PLP) and European Parliamentary Labour Party having 51 MPs/MEPs?
query: What is the significance of 51 MPs/MEPs in the 2016 Labour Party leadership election?
answer: In the 2016 Labour Party leadership election, challengers needed nominations from at least 20% of the combined membership of the Parliamentary Labour Party (PLP) and European Parliamentary Labour Party (EPLP), which totalled 51 MPs/MEPs, to be included on the ballot.