"Be mother" - Etymology and usage

I recently came across the idiom "Be mother" in a crossword. It is supposed to mean 'to pour tea'. I was surprised by the meaning, and want to ask if there is any etymology or history behind this curious idiom. Is it informal/facetious/slang?

Solution 1:

It's normally heard as Shall I be mother? meaning 'Shall I pour the tea?' It's used because pouring the tea has traditionally been seen as a mother's role. I suspect it's now heard less than it once was for various social rather than linguistic reasons. It's not slang and it's not facetious, but because of the nature of tea-drinking it's likely to be heard in informal situations.

Solution 2:

It is also a saying that stems from the superstition that a female guest should never pour the tea in another woman's household - for then she would fall pregnant.

So should a woman offer to pour the tea in another woman's household ("I'll be mother"), she desires to become a mother. Or it may also be used as tongue-in-cheek by those who are not in the least superstitious.

From author and folk historian Dr. Alec Gill:

Tea-drinking and fertility were intermingled. Indeed, the tea-pouring clich‚ "I'll be Mother" stems directly from primitive superstition. The consequences of two people pouring from the same pot could be dire.

During the 1930s, if a man and woman took turns in pouring, a child would be born to them. A female visitor must not pour tea in another woman's house - otherwise, she would fall pregnant. This evolved to having twins and - even worse at the superstitious level - ginger-headed twins.

Thus, an early form of birth-control was to let only one person do all the pouring in company!