EE said it will take Ofcom to court if the regulator doesn’t reverse a decision to set a spectrum cap on upcoming 4G and 5G auctions, a move which was backed by O2 UK.

Ofcom in July announced plans to impose a cap of 340MHz on all UK operators for spectrum expected to be usable by 2020 in an attempt to reduce the share held by EE, the country’s largest asset holder, and its parent company BT.

At the time, O2 UK and 3 UK said the measure fell short, while EE believed it was unnecessary.

Earlier this month 3 prepared to launch a legal challenge against Ofcom’s rules, which it said failed to address competition concerns.

3 is a long-term critic of the division of spectrum in the UK, and threatened action if Ofcom failed to address the market dominance of BT and Vodafone with its auction rules.

As the UK’s auctions for 4G and 5G spectrum were scheduled to be held by the end of 2017, legal action would significantly delay the allocation process.

While EE accepted Ofcom’s cap for 4G, the operator wants to be able to take part in the auction for the most up-to-date 5G spectrum.

An EE company representative said: “In response to 3’s action, we have made the difficult decision to challenge the proposed structure of the next auction of mobile spectrum. We need to protect our customers’ mobile experience, and help build the platform for the UK to have the highest quality 5G networks.”

According to Financial Times, Ofcom said any legal action puts the future of mobile data at risk by potentially delaying the issue of new spectrum and airwaves. The regulator warned of a potential knock-on effect on the rollout of 5G services, which have already been held up by 3’s attempted acquisition of O2, owned by Telefonica.

Meanwhile, O2 CEO Mark Evans said 3’s “legal action will inevitably cause delay to the auction and gives no thought to the impact and harm this will have to UK customers, companies and economic growth.”

In a statement, Evans said he believes any litigation must be swiftly dealt with, and Ofcom should press on with its auction plans “either on a permanent or temporary basis” to enable “spectrum to be used whilst a potentially protracted legal process in relation to the 3.4GHz spectrum is contested.”

“This country desperately needs more mobile airwaves. It is possible to hold the 2.3GHz auction now and grant immediate access to the newly-available spectrum. Ofcom can and must act,” he added.

According to GSMA Intelligence, EE led the UK market with a 32 per cent market share in Q2 2017, followed by O2 (30 per cent), Vodafone (24 per cent) and 3 (13 per cent).