News that Le Café Alain Ducasse, at the Coal Drops Yard complex in King’s Cross in London, is now serving “the perfect cup of coffee” (their words) at £15 a pop has – to be diplomatic – divided opinion. While it may be tempting to see in that price-tag proof that some people have more money than sense, it still doesn’t make Ducasse the Chanel of baristas. Even Starbucks can break the bank. (Remember when, back in 2013, a man paid $47.30 for a 48-shot “quadriginoctuple frap” – 48 shots with a busload of extras.)

Ducasse’s beans are from Yemen; the price reflects the challenges of growing coffee – let alone harvesting, processing and exporting the beans – in war-zone conditions, and paying fair wages for it.

“We’re not there to try to negotiate the prices down, but to pay the farmers more,” says AJ Kinnell, director of Monmouth Coffee Company, which has campaigned for ethical coffee since the late 1970s. As for what else goes into the price, beyond the raw ingredient: there’s labour (which, already in 2013, made up nearly a quarter of the price), rent, utilities, cups, crockery, equipment such as grinders and espresso machines, milk and, of course, says Kinnell, “the other milks that aren’t milk”. All throw up ethical questions, and often increase expense. A central London roastery will charge more than a coffee shop in a Yorkshire village if only because of their rents.

The price also depends on the kind of coffee, says the British Coffee Association’s Chris Stemman, with high-end small-batch microlots selling for what he calls crazy sums: “Eighty dollars a pound is not unusual.” But someone, somewhere, will pay that like they do for wine or cheese because they find value in it.

Most coffee is traded in US dollars, meaning the price paid by British importers is affected by any market volatility – such as the Brexit vote, which caused a 13% drop in the value of sterling. With most of the UK’s coffee imported from the EU, Brexit itself could be even worse. If we crash out with no deal, says Stemman, roast and ground beans will be hit with tariffs of more than 7%.

And if you were thinking you would just stay home: the price of instant coffee – comprising two-thirds of the 95m cups consumed daily in the UK – is also expected to rise by 9%.

• This article was amended on 7 March 2019. The value of sterling fell by 13% after the Brexit referendum, not 20% as an earlier version said.