i saw this phrase (pls ignore the full stop in f.a.g) used on forum or a paper but don't really understand what it means. Would appreciate if someone could tell me.

an example on the forum: Person A said: any team news?. Person B replied: No back of the f.a.g packet prediction from me today, apparently the manager Bingo ball machine has broken down so he is havng to really think about his team selection for tonights game and do it the old fashioned way.

an example on a paper: Conservatives criticise 'f.a.g packet' enterprise zones
The Welsh Government has been accused of rushing out an announcement about nurturing businesses.
Conservative assembly leader Andrew RT Davies said the government's enterprise zones policy had been made up "on the back of a f.a.g packet"
"Back of the *** packet" is apparently a British equivalent to the American "back-of-the-envelope" which is an adjective almost universally applied to highly informal writing or calculation, often done in haste, not intended for wide use.
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C Snyder, wholeheartedly thank you for your instant reply
but pls forgive that I don't quite get your reply. Were "often done in haste, not intended for wide use" the meaning for the phrase or a situation of it being used? That means if the noun phrase "back of the f.a.g packet" means something done in haste and not intended for wide use? Or they are just like "highly informal writing or calculation" being the situation when we use this noun phrase?
They were adjectival phrases further describing the phrase "highly informal writing or calculation".
C Snyder, I get it, thanks
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A F.a.g. Packet is a cigarette carton. f.a.g. (minus the full stop) is a slang word for a cigarette in the UK. hence, when an engineer needed to show a colleague a quick sketch, he would often draw it on the back of his cigarette carton, or f.a.g. packet.

It's always incorrect to use any full stops/periods when writing 'fag' – whatever meaning the word has in the sentence.

The definition is very similar to the one already put forward, as in a rushed calculation, not meant to be taken as absolutely accurate or to be fully relied upon.

But there is no need for the full stops between the letters in the word "fag", as certainly in the UK, the word fag simply means a cigarette and nothing more.

I know it has other conatations in other countries, especially the US, but it is purely a UK term and so I'd suggest that it doesn't need "protecting" by splitting it up.

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