Sara Hagemann, a Danish analyst with the Brussels-based European Policy Centre adds that extreme parties would get a much higher proportion of seats than in national elections. "Voters who turn out [in European elections] often have quite strong opinions about the EU," she says.
Though elections to the European Parliament habitually throw up a protest vote, this time around they could prove fatal to governments in at least two countries if the ruling elite perform as badly as predicted. Hungary's ruling socialists are so unpopular that a bad result could see their government fall apart.
But no leader is more vulnerable than Britain's Gordon Brown, who has seen support ebb not just from his Labour Party voters but from his own ministers. The Labour government, humiliated by revelations of mercenary expense claims by legislators, may struggle to stay afloat much longer if overall results are as poor as some predict.
On Friday, Brown was forced to reshuffle his remaining ministers after four big names quit in 72 hours. A terrible result when voting tallies are announced on Sunday evening could be the final straw, experts say.
"The results are going to be very bad for Labour; the question is, will they be disastrous," says Professor Grant. "If he's got 20 percent of vote, though bad, that will be seen as just enough. The problem is if he went as low as 16 percent," which could leave Labour in fourth place and Brown's mandate looking anachronistic.
A giant election, but does anybody care?