High pressure side of the fuel pump (the pump is in the tank, accessed through a round hatch in the boot floor), may be giving up - when you switch the ignition on to position2, can you hear the pump whine ?
Immobiliser - they can play silly-beggars. Try locking and unlocking (using the remote). Mine has done this a few times - normally when parked near to big VW 4x4's :?
Is it an auto 'box - the start inhibitor switch might be playing up. The switch only lets the vehicle start when in 'park' or 'neutral'