Originally the show used to start in the Autumn, which I think is the ideal time for a show with scares in.

When the cold weather comes in people want to huddle inside, in the dark and be spooked as a family unit.

I gather the thinking behind the move to a Spring start was to maximise DVD sales (there are the individual discs sold quite close to the time of broadcast and the box sets and the soundtrack which gets a publicity boost from the Christmas special trails).

Hopefully the Autumn half will be a success and encourage the producers to revert back to a full Autumn series ending at Christmas (and perhaps swapping the Christmas special with an Easter Special).