I believe I do have a timeline of events that you might find elucidative.
During his National Service with the British Army, Jerry visits a shop near to where he is posted in Germany. He meets Hilla, who is working in the shop.
Jerry’s original reason for visiting the shop was to purchase a rubber stamp that could replicate a mark that he shows on his hand. This mark is to prove that he has completed a cross-country run, a task which he wishes to avoid in future.
Hilla says that her father could make the stamp, but questions why he should help a British soldier. When Jerry asks if this is because her father is still sore about losing the war, Hilla responds: “No, Solomon Goldfarb is not sorry that Germany lost the war.”
After more back-and-forth between the two, Jerry comes to the suggestion that he should save his money on the rubber stamp and instead buy tickets to the pictures for Hilla and him.
The Wilkinson family pull Christmas crackers around the table, starting with Vanessa and Uncle Newt. Vanessa wins and immediately takes the hat from inside and rips it up.
She also gets a small plastic cowboy from the cracker, which she gives to her grandson, Benji. Benji is warned not to snatch by his mother, Hilla, who reminds him that “Level 3” behaviour is expected.
Jerry says “onwards and upwards” and nominates Deborah to pull the next cracker.
Deborah chooses to pull her cracker with her grandfather, Walter. Vanessa indicates to Walter that his cracker is on his side plate. Deborah wins, but questions if she has to rip up her hat. She asks if that tradition comes from them being a bit Jewish.
Hilla tells her that lighting the candles is because they are a bit Jewish, but that the hat ripping comes from the Wilkinson side. It transpires that the tradition dates back at least as far as Uncle Newt’s childhood.
Uncle Newt prepares to tell the story of why the family rip the hats, but he is interrupted by a kitchen timer. Hilla bustles out of the room to fetch the pudding, enlisting help from Myra.