The RAF name seems fixed.
Note the last 2 paragraphs:
PICTURES: Cameron welcomes RAF's last C-17 to Brize Norton
The C-17 fleet will from late this year be joined at Brize Norton by the RAF's first of 14 Airbus A330-200-based Future Strategic Tanker Aircraft. The base will also eventually house 22 Airbus Military A400Ms, with the type to be named the "Atlas" in UK service.
The RAF expects the A400M to achieve its in-service date during 2015, with the milestone to be declared with the availability of its seventh aircraft.
Atlas C.1, it seems.