Weight / Fat loss

So without sounding like an idiot is it possible for you to have a very low carb diet whilst still being able to cycle big distances. Would you body not start using your fat reserves if it had no carbs to burn?

Not really - your body can't burn its own fat fast enough to keep you supplied with energy on a long ride. You need to load up the carbohydrates before, during and after if you want to ride long distances.