BT faces a showdown with telecoms watchdogs in Brussels after Ofcom triggered formal proceedings to enforce a legal split with with its network unit, Openreach.

A rival operator warned of “fury” in the UK if the EU sought to overrule Ofcom and block the decision as Britain prepares to exit the bloc.

The regulator said BT had failed to come up with voluntary reforms that would make Openreach independent enough to deliver much-needed improvements to Britain’s broadband infrastructure.

BT has been in negotiations with Ofcom since the summer but has failed to reach agreement over how much autonomy its network unit will have over its spending, staff and assets.

Talks have reached deadlock, with BT proposing a chairman for Openreach who would report to the BT board, threatening its independence in the eyes of regulators and rivals Sky, TalkTalk and Vodafone.

Under its current structure, Openreach provides wholesale broadband service on equal terms to BT and its competitors in the retail broadband market.