I believe

Reuben had been working on his project since March. He was about to prove that Father Christmas was a hoax. It was the big night, Christmas Eve, all quiet in the house except a little mouse stirring his midnight cup of tea.

Reuben had fallen asleep but the Spy Cam was set up and trained on the Fireplace, where a pair of boots appeared and then the man himself.

With a brisk efficiency Santa drained the sherry glass, enjoyed the mince pie, stashed presents in stockings, straightened a picture, deleted the evidence off the camera and returned up the chimney.