Harold Wilson clarified in 1974 (HC Deb 20 December 1974 vol 883 cc711-2W):
Mr. Maxwell-Hyslop asked the Prime Minister whether he will make it the practice of his administration that when Ministers employ the word “billion” in any official speeches, documents, or answers to Parliamentary Questions, they will, to avoid confusion, only do so in its British meaning of 1 million million and not in the sense in which it is used in the United States of America, which uses the term “billion” to mean 1,000 million.
The Prime Minister: No. The word “billion” is now used internationally to mean 1,000 million and it would be confusing if British Ministers were to use it in any other sense. I accept that it could still be interpreted in this country as 1 million million and I shall ask my colleagues to ensure that, if they do use it, there should be no ambiguity as to its meaning.
(Spotted thanks to Paul Bolton and Richard Cracknell’s 2009 Commons Library Briefing.)
Nice example of social construction and maybe a speech act:
As a first approximation, speech acts are those acts that can (though need not) be performed by saying that one is doing so. On this conception, resigning, promising, asserting and asking are all speech acts, while convincing, insulting and growing six inches are not. One can, for instance, resign by saying, “I resign…”, although one can also resign from a position without describing oneself as doing so.
Not sure whether it was actually a speech act – to discuss.