I use a combination of Infinit and water/Gu for 2 hour+ workouts and all races. Although Gu does not have the level of electrolytes that I need for long distance events. I use water for anything shorter than 2 hours–except maybe the occasional intense 1.5 hour TT.
Unless you’re willing to delve into the details of nutrition, I recommend sticking to a reputable energy drink provider like Gatorade Endurance or Infinit. Personally, it’s hard enough for me to find time to fit 10 to 20 hours of training into my week. I don’t care to mess around with saving a few bucks making my own drink–which may or may not be functional.
Check it out… http://www.infinitnutrition.com/. They cover the UK, too.