Belgium goes to the polls on Sunday in what will be a bitterly-contested election, with the likely winner and possible new prime minister a Flemish nationalist dedicated to the breakup of the country.

The early election – triggered by the collapse of the outgoing government over a failure to resolve the long-running linguistic dispute that is the faultline in Belgium's survival prospects – has been uncommonly divisive thanks to the emergence of mainstream Flemish separatists as the strongest political force in the country.

Split into Dutch-speaking Flanders, to the north, and francophone Wallonia, to the south – with Brussels straddling the middle and gluing the country together – Belgium is predicted to be on the road to a protracted "velvet divorce", in the style of the former Czechoslovakia, following the ballot.

Bart de Wever, the leader of the separatist New Flemish Alliance, represents a new breed of popular Flemish nationalism.

His party is running at 26% in the opinion polls, ahead of all contenders. Flanders is the bigger half of the country, and the prime minister is usually the leading Flemish politician.

Until a few years ago, Flemish separatism was led by the racist, extreme-right Flemish Interest party, which was quarantined by mainstream politics.

But Flemish separatism now enjoys a plurality of support in Flanders, with De Wever leading the pack.

A poll in the France Soir newspaper this week found that, should Belgium fall apart, a comfortable majority of French people would be happy to annex Wallonia.

The anxiety over Belgium's longevity was also underscored this week by media coverage of rumours that Nato could move its Brussels headquarters to Germany – reports that were instantly denied by Nato officials.

While Flanders is likely to vote mainly for the separatist centre right, Wallonia will veer to the left, with the socialists certain to win there.

Both parts of the country vote for their own parties, none of them bridging the linguistic divide. De Wever's 26% nationally in the polls translates into 45% support in Flanders.

The likely outcome is gridlock of a type that brought down the outgoing government, led by the Flemish Christian democrat Yves Leterme, and months of haggling over a new cabinet.

Belgium takes over the EU's rotating presidency at the end of the month, but it is likely to be without a proper government for most of the summer.