Can members of the European Parliament (EP) be held accountable under the EP's current electoral system? A working accountability-control relationship between members of parliament and voters predisposes a reasonable degree of awareness about voting patterns in parliament as well as how these patterns relate to the policy preferences parties communicate to the electorate. In the EP case, this relationship is significantly more complex than in the context of national elections. This is because European elections are not a single election, but the sum of separated elections taking place simultaneously in each member state. Hence, MEPs face a trade-off between sticking to their campaign promises and responding to the position of their European Parliament Group (EPG).

This paper analyses the relationship between the cohesion of EPGs and the policy platforms (manifestos) published prior to European elections by the national parties that form EPGs. Given the relatively low level of public attention paid to how winning coalitions in the EP form in individual votes, EPGs could under certain circumstances be incentivised to use the policy platforms of their constitutive parties to signal to the latter ones' constituencies. We posit that more diverse party manifesto positions generally result in reduced cohesion of MEP votes within European party groups. We explore this and other hypotheses via quantitative analysis combining data from the EP voting record and the Euro-Manifesto project. We also consider changes in policy platforms of individual parties that are induced by adopting new platforms during a campaign for elections on national level.