Hi UK too
20-100g Caster sugar (I use a protein scoop for ease, levelled is 60g carbs and 1L bottles - up to 90-100g/bottle)
1 x Heaped Tsp. Trisodium Citrate (Salt - not the table variety).
1 x Heaped Tsp. Citric acid.
Optional - 1 x Heaped Tsp. Bulk.com hydration mix for flavour (any flavoured sports drink or I even use orange/blackcurrant squash sometimes).