> Virtually all artificially sweetened soft drinks in the Uk are sweetened with aspartame

A quick look at a few soft drinks I could think of, and their UK sweeteners:

  Fanta: Aspartame, Acesulfame 
  Coke Zero: Aspartame, Acesulfame-K, Enzymatically Produced Steviol Glycosides
  Pepsi: Acesulfame K, Sucralose
  Irn Bru: Aspartame, Acesulfame K
  Tizer: Acesulfame K, Sucralose
  Old Jamaica Ginger Beer: Sucralose
  Lipton Iced Tea: Steviol Glycosides from Stevia
  Ribena: acesulfame K, Sucralose

There seem to be no clear winners, with the most noticeable finding that multiple ones are usually used.