When do British people use the word "cookie"?

As far as I know they always call cookies biscuits and I have heard them refer to cookie jars as biscuit tins. But perhaps through media coverage we are all being exposed to other culture's use of words. The sportscaster has perhaps had that certain phrase introduced into his vocabulary. Thanks to the internet/media, we now have the pleasure of hearing how other cultures use language and that surely intertwines into how we use it too.

We do still say 'biscuit' in normal speech and our supermarkets, even the one owned by Walmart, still have biscuit aisles. However we are widely exposed to American culture and in the context of sports commentary "raiding the cookie jar" does work better than "raiding the biscuit tin": somehow "raiding the biscuit tin" just feels much more petty. This is perhaps because, although there is an overlap, an American style cookie tends to be bigger, softer and generally more indulgent than a British biscuit. In fact large, soft, special treat biscuits are sometimes sold as 'cookies' although they are usually so large we would probably not think of them as a 'biscuit' anyway.

Having said that Americanisms do appear in proper English, especially when promoted by American companies. Following the penetration of the British market by McDonalds and Starbucks most vendors of coffee, including iconic British brands, now offer 'regular' cups rather than 'standard' or 'medium'. That is unless they aspire to Italian sophistication and call them 'medio'.

One area where you will hear 'cookie', though, is computing. Small files downloaded to your computer by websites are always called 'cookies'. I can't imagine any British person wanting to change that. In fact most users probably don't even make the connection between leaving the file and presenting a child with a biscuit.

As a British person, I have always known (and use) the expression

That's the way the cookie crumbles.

given by the Oxford Dictionaries as a North American phrase. However I never buy cookies — even when that word is on the packet — but biscuits.

One British term for a cookie jar is

biscuit barrel
NOUN

British
A small barrel-shaped container for biscuits.

I don't know anybody who keeps biscuits in a jar.

Okay, I think we have an answer, but unfortunately what has been posted is not very cogent, so I will sum up:

The British call cookies "biscuits". They occasionally use the word "cookie" in the context of using Americanisms like "he got caught with his hand in the cookie jar", or "that's the way the cookie crumbles".

In the UK a cookie is a particular type of biscuit with a high butter and sugar content so the dough melts during cooking giving a crispy edge with a softer centre. Biscuit covers a wide range of recipes from sweet, semi-sweet, to savoury e.g. "biscuit for cheese" with a wide range a textures, shape thickness. Basically a baked good with aa element of crispy A cookie is a biscuit, not all biscuits are cookies