Why is “Meryl Streep” always holding oranges in “The Strike”?

Apparently, it was based on something Jennifer Saunders read...

Saunders: ‘So many weird layers. The peeling of the orange when I was playing Meryl Streep playing Mrs Scargill was based on something I read about Streep, that she had this knack for pulling focus, even when she didn’t have a line in the scene.

^Source

If an actor is eating an orange, it is a way of upstaging and taking the focus off the main actor in the scene. Oranges are very evocative fruit - if you see one being peeled, you know how it will taste and smell, sometimes your mouth will start watering in anticipation. It's hard to ignore an orange.

In the Comic Strip Presents...The Strike, Jennifer Saunders was playing "Meryl Streep" as an actress who has to have all the attention, even if she wasn't the main character. Peeling an orange is a way to focus attention on herself, while not overtly upstaging the main character in that scene. This is played as a quirk of the actress, not the character, as shown by the dailies-watching scene where she is still peeling oranges. (Also it is unlikely that a poor miner would have a bowl of oranges on the table!)

This is a caricature of Meryl Streep, so minor traits are exaggerated.

When thinking about movies and oranges, Francis Ford Coppola comes to mind (As laranjas eram um uso intencional do simbolismo pelos cineastas?). It is argued that the use of oranges in scenes forshadows imminent death or desasters. Some directors (such as Guy Richie) like to give a nod to FFC by placing oranges in some of their movies.

Maybe this is one of those cases. But given the time, it might just be a coincidence.