O2 revealed as Ofcom’s main service provider for mobile connectivity.

Ofcom the independent regulator and competition authority for the UK communications industries has over 95% of their staff contracts with O2.
Revealed by a freedom of information request by Mobile, Ofcom assured all contracts were subject to the Crown Commercial Services Framework to ensure fair bidding and competition on prices for all prospective suppliers. Even so out of the 537 contracts for both mobile and data connectivity O2 were awarded 514, with 13 to Vodafone a further nine for T-Mobile and just one for EE.
Ofcom confirmed ‘The main corporate service provider for Ofcom is O2. We also use EE, Vodafone and T-Mobile to ensure coverage for colleagues who are unable to obtain an O2 signal at their home location. The average annual spend (over the past three years) is around £175,000’ (Mobile)