The European Commission has launched “infringement proceedings” against Britain after Boris Johnson refused to nominate a new British EU commissioner.
In a statement, the commission said that it considered that the UK was “in breach of its EU treaty obligations”.
It said that the Government had until November 22 to respond to the notice.
Mr Johnson has repeatedly said he would not appoint a new commissioner – even though all member states are legally obliged to do so.
Incoming commission president Ursula von der Leyen has said she wants to form a new College of Commissioners on December 1.
But in a letter to the commission on Wednesday, the Government said official pre-election guidance meant it could not make international appointments ahead of polling day on December 12.
In its response, the commission said that under EU case-law, a member state “may not invoke provisions prevailing in its domestic legal system to justify failure to observe obligations arising under union law”.
The launch of infringement proceedings could be the first step on referring the case to the European Court of Justice.
However, Mr Johnson may well calculate that by the time it reaches that stage, Britain will be out of the EU – at least if he is able to deliver Brexit by the latest deadline of January 31.
The greater danger for the Government may be that it will sour forthcoming negotiations with Brussels if the refusal to appoint a UK commissioner delays the formation of the new commission.