>Am not entirely convinced by the neutral thing though because that might cause more
>fuel to be used keeping the engine ticking over, rather than letting the car's
>momentum achieve this?
While it's true that neutral uses some fuel to keep spinning, whereas in-gear uses no fuel, the problem is that when you are in-gear you are engine-braking and hence slow down quicker (due to the friction etc of keeping the engine spinning at high revs). So the total energy loss is greater in-gear than in neutral. Hence if you want to slow down (engine-brake), in-gear is best. But if you want to keep moving, then neutral is best.
Take a look at page 3 of the following link: