Specification F.155T was for a high altitude supersonic interceptor to supplement the Lightning, which was only intended be a point defence fighter. By 1957 the competing designs had been narrowed down to the Fairy Delta 3 and the Armstrong Whitworth AW169. Some of the other contenders were truly enormous; the Saunders Roe SR.187 being 84ft long and weighing around 98000lb!
Of course the wretched Duncan Sandys scuppered any further development with his infamous White Paper, leaving the RAF with the Hunter, Javelin and Lightning.