Mix well the Thunderbird with the Vodka and pour into an empty litre coke/lemonade bottle. The exact ratio of vodka:thunderbird can be altered to the creator's taste. Fridge for at least 12 hours.
Donnington Brainstorm is best at temperatures between 2-4 degrees centigrade. If the drink is too cold it will tend to be too bitter; if it is too warm, it will tend to be too sweet. At just the right temperature, it should be light, refreshing, slightly peary and the alcohol taste minimal.