Viktor Orban, the Hungarian Prime Minister, faces calls to distance himself from an anti-immigration campaign or see his Fidesz party thrown out of the European Union’s most powerful political grouping on Wednesday.

The European People’s Party (EPP), a bloc of conservative parties from across the EU, is set to meet in Brussels this on Wednesday evening to decide whether to expel Fidesz over campaign posters that attacked Jean-Claude Juncker, the president of the European Commission.

Manfred Weber, the German favourite to succeed Mr Juncker, flew into Budapest last week in a bid to shore up an increasingly strained political alliance with Mr Orban.

As Mr Weber drove into the city, the campaign…