Current and past meaning of "billion" in BrE

Question

According to the following extract from the ODO "billion" in BrE used to mean "a million million", but its meaning has changed to the more common AmE usage meaning "a thousand million".

• In British English, a billion used to be equivalent to a million million (i.e. 1,000,000,000,000), while in American English it has always equated to a thousand million (i.e. 1,000,000,000). British English has now adopted the American figure, though, so that a billion equals a thousand million in both varieties of English.

The origin of this usage and its subsequent change, as explained by Etymonline, are from French:

• 1680s, from French billion (originally byllion in Chuquet's unpublished "Le Triparty en la Science des Nombres," 1484; copied by De la Roche, 1520); see bi- "two" + million. A million million in Britain and Germany (numeration by groups of sixes), which was the original sense; subsequently altered in French to "a thousand million" (numeration by groups of threes) and picked up in that form in U.S., "due in part to French influence after the Revolutionary War" [David E. Smith, "History of Mathematics," 1925].

• France then reverted to the original meaning in 1948. British usage is truer to the etymology, but U.S. sense is said to be increasingly common there in technical writing.

As far as I can remember (1980s), a billion, at least in finance, has always meant a thousand million, and I've never come across its older usage.

Questions:

• When did BrE adopted the AmE usage of a billion?

• What was "a thousand million" called in BrE when a billion meant "a milliom million"?

Answer 1

Britain officially changed to the short scale system in 1974

source: http://hansard.millbanksystems.com/written_answers/1974/dec/20/billion-definition#S5CV0883P0_19741220_CWA_439

However, I would assume that the American usage had gained quite some popularity before this point otherwise its adoption wouldn't have been necessary.

The term you are looking for is milliard.

Answer 2

I can't back this up, but I wonder if it is linked to increasing use of engineering notation and metric prefixis, which would make it more important to have a specific name for every multiple of a thousand. This would make "thousand million" undesirable, forcing a choice between adopting the American billion and the French milliard.

https://en.wikipedia.org/wiki/Engineering_notation

https://en.wikipedia.org/wiki/Metric_prefix

Answer 3

I was taught that a billion was a million million, but gave up on that years ago due to American usage. It's now a thousand million, or 10^9, or in old language, a milliard.

Usage of milliard would appear to have been declining since the 60s, as suggested by google ngrams:

https://books.google.com/ngrams/graph?content=milliard&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cmilliard%3B%2Cc0

As an academic writer I would say that there's no clear cut-off. Older people will continue to complain about incorrect usage; younger people will continue to adopt the newer terminology -- until the old people die.