Good shout. There’s probably class differences too - there usually are.

Tbh, I was hoping some other Brit with actual social skills would drop by with the answer, then I could pretend to have known all along. I think it indicates increasing familiarity, something like

1. Tea - you are a person who might want tea
2. Cuppa - we are on friendly terms and I consider you my social equal
3. Brew - I would trust you with my life and call you wanker to your face

In lesson 2, the semantics of tea vs brew vs cuppa

Boys? Don’t dig deeper than you are tall, ok? Sand can fall in on itself. If it’s up to your neck, we dig you out. If it’s over your head, we don’t get to come to the beach again.

Got that, boys? Okay. Grab a spade.