The licences are held by EE, Three UK and Virgin Media 02.
The unpaired part of the 2100MHz band was originally auctioned off in April 2000 to support the rollout of 3G mobile broadband networks.
All four of the major MNOs currently use the paired radio spectrum in the 2100MHz band.
But the slice of unpaired part of that same band is largely unused and the operators don't have any plans to deploy higher-power services in the spectrum. This is primarily due to the lack of a supportive ecosystem, as well as the need for a guard band against paired spectrum, which is used to reduce the risk of interference, and the limited bandwidth it offers.
Ofcom is looking to ensure optimal use of the unpaired 2100MHz spectrum, which resulted in its decision at the end of 2023 to revoke all existing licences. The regulator said that the spectrum that will be freed could be better used by the emergency services, railways or the utilities sector.
Ofcom has formally given five years' notice to the operators that their licences will be revoked.