O2 (UK) they can do it too" in reference to Vodafone and EE, O2's biggest competitors and the UK's top three mobile-telecoms companies. O2 (UK) Telefónica UK Limited (trading as O2 – stylised as O) is a telecommunications services provider in the United Kingdom, owned by the Spanish multinational Telefónica, and is headquartered in Slough. With 25 million subscribers (as of December 2017), O2 is the second-largest mobile network operator in the United Kingdom after EE, with Vodafone in third place. O2 was formed in 1985 as Cellnet, a 60:40 joint venture between BT Group and Securicor. In 1999, BT Group acquired
LSWR O2 class to gain acceleration on intensive timetables. Adams settled upon the 0-4-4T wheel arrangement to provide the basis of what was to become the O2 Class. The second of William Adam's 0-4-4 designs, the O2 Class was a development of his previous T1 class of 1888. The brief behind the design was to create a locomotive capable of mixed-traffic operations, a characteristic dictated by the relatively small wheel diameter and smaller cylinders, effectively to replace the obsolete Beattie Well Tank. As a result, a compact locomotive with high route availability was produced, a factor that would be essential during the later