Lawyers for the European Union on Tuesday told an arbitration tribunal that Britain's ban of fishing for sandeels in its North Sea waters breached an agreement on fishing rights both sides struck after Brexit.

The EU and UK face their first post-Brexit legal showdown as the bloc challenges Britain's North Sea sandeel fishing ban – a minor environmental case with major political implications.

The UK has banned European vessels from catching the silvery fish species in its North Sea waters but the EU is challenging the move.

A tiny silver fish which is an important food source in the North Sea will take centre stage Tuesday as the European Union and Britain square off over post-Brexit fishing

The tiny sand eel is used widely as bait and in animal feed — but it's also an important food source for puffins and other seabirds.