About 30 years ago, Bruce Williams had a homebrew supply shop in Alloa, Scotland. Now and again, customers would travel in from far-off places like the Outer Hebrides or isolated parts of the Scottish Highlands, bringing with them stories about old beers that they remembered their grandparents brewing – made from recipes that had been handed down through the generations.
Many were hoping to use all sorts of ingredients that Williams had not thought of putting in beer before. One was heather. It gives the beer a sort of astringency – a dryness, especially when you open your mouth after taking a sip – and adds a herby woodiness to the flavour. Millions of acres of heather have blanketed the country's moors since the Stone Age, so it is quite conceivable that, if brewers experimented with local plants and other resources thousands of years ago, they would have used it as an ingredient to flavour ale.
Few would dispute that heather ale has been made for centuries in Scotland. It has even been romanticised in a poem by Robert Louis Stevenson. We are also more or less certain that British brewing of some form was going on as far back as the Romans and that mead – a fermented honey drink – has been quaffed here for hundreds of years.
But how far back, specifically, does beer-making go in Britain? Do archaeological records reveal what beverages Britons were drinking as far back as the Neolithic – the era roughly between 6,000 and 4,500 years ago?
Famously, one 1980s archaeological dig at Kinloch on the Outer Hebrides' Isle of Rhum found apparent residue from a long-evaporated beverage. The pottery it came from dated back about 4,000 years. Microscopic analysis detected pollen grains, which suggested high levels of heather, and some meadowsweet and royal fern.
Meadowsweet may simply have been added in order to counteract the smell of decaying flesh
"If you regarded them as a recipe, then you can ask 'what would they make'," says Caroline Wickham-Jones, one of the excavation's archaeologists. "And one of the things was heather ale as a fermented drink – but it might easily have been a mouthwash or something."
Still, Wickham-Jones and her team enlisted the help of a Glenfiddich distillery to brew a new ale inspired by this potential recipe. "It was fabulous," she says.
Traces of meadowsweet have also been found in Neolithic beakers at Aberdeenshire and Fife. Still, the Fife specimen was found in a burial site and Alison Sheridan, the early prehistory curator at National Museums Scotland, notes that meadowsweet may simply have been added in order to counteract the smell of decaying flesh.
Meanwhile, large pots and evidence of heat-cracked stones have been found at Skara Brae, a 5,000-year-old settlement in the Orkney islands just north-east of Scotland.
Local archaeologist Merryn Dineley believes that pottery was once used for heating malt – the germinated and heated cereal grains that ferment to produce alcohol. Dineley has experimented with Neolithic-style equipment and argues that malting of grains could have occurred in this period.
If you've got sprouted barley, that's good evidence for beer production
But proving, conclusively, that specific alcoholic beverages were drunk as far back as the Neolithic is extraordinarily difficult if not impossible, says Jessica Smyth, an archaeologist and chemist at University College Dublin. For example, chemical analysis of residues can never provide complete proof that an alcoholic beverage was once held in a vessel. Alcohol can evaporate within days or weeks, never mind millennia.
"You get lots of generic molecules, lipid compounds for example, but you find them in everything – you can't generally say it comes from this specific product," says Smyth. Sometimes barley lipids appear to be present in old earthenware, for instance, but Smyth says the concentrations are so small that tying the lipids to that specific plant becomes tricky.
Consider calcium oxalate, which is often cited as evidence for alcohol because it is a by-product of the brewing process. "Mineral salts are extremely common," says Smyth. "You just can't say that that is definitely part of an ancient brewing process."
Other finds are more persuasive.
"If you've got sprouted barley, that's good evidence for beer production," says Oliver Craig, an expert in biomolecular archaeology at the University of York. But such confirmation is difficult to find at pre-Roman sites in Britain.
The find has been described as the first written record of brewing in London
There is even a theory that during the Neolithic period, Britons had a shortage of cereal grains for several hundred years due to climatic changes between 5,300 and 4,400 years ago. This is according to University College, London archaeologist Chris Stevens.
But aside from ales brewed with fermented grain, it is entirely possible that early Britons were fermenting honey to make early forms of mead.
In fact, the heather "ale" that may have been drunk at Kinloch would more likely have been of this type, Wickham-Jones says.
Once the Roman era arrives, more evidence begins to crop up to support the idea that ales were widely brewed in the British Isles.
At a building site in London, 2,000-year-old wooden writing tablets have been discovered. They mention a "maltster" or "brewer" named Tertius. The find has been described as the first written record of brewing in London.
A lot of time, effort and wealth were put into these vessels – they clearly just weren't drinking water out of them
There are also references to brewing at a famous Roman site, Vindolanda, in the north of England.
"There's a letter from an officer asking for more ale for his troops – it's hard to tell whether he's drinking with them or not," says Joshua Driscoll, a PhD student in anthropology at the University of Wisconsin-Milwaukee. It is widely believed that Romans were importing wine to British forts in amphorae.
"Some people might extrapolate from that that you had officers drinking wine and soldiers drinking ale," says Driscoll.
The design of drinking vessels also hints that Roman and Medieval Brits were drinking alcoholic beverages, says Jonathan Horn, an archaeologist at the University of Edinburgh.
Horn has studied tankards dating from the British Iron Age, the period from roughly 2,800 to 1,900 years ago. The tankards have interesting forms. Some are like little barrels, for instance, and are often ornamented with intricate metalwork and small handles.
It is easy to imagine why early societies would have made the effort to produce alcoholic drinks
"A lot of time, effort and wealth were put into these vessels – they clearly just weren't drinking water out of them," says Horn. "We see basically an uptake of these native vessels, specifically, within the Roman army. They're clearly taking on the native drinking culture."
By about 1,600 years ago, ale drinking was widespread. Excavations have revealed the remains of 800-year-old malting ovens and other brewing apparatus. And alcoholic beverages are routinely mentioned in some of the great poetry of the era – including the Anglo-Saxon epic Beowulf, written over the period from 1,300 to 1,000 years ago.
As part of his home-brewing experiments, Bruce Williams spent hours poring over records in Glasgow University's Scottish Brewing Archives, getting inspiration for other types of beer. The earliest recipes he could find dated back to the 12th and 13th Centuries. He says heather is mentioned in some of the oldest records.
But it was only at the very end of the medieval period that hops began to be widely used for the drink that we recognise today as beer.
For thousands of years, other ingredients must have provided the basis for flavour. Even if we cannot be sure what they were, it is easy to imagine why early societies would have made the effort to produce alcoholic drinks in the first place.
"Alcohol was intimately tied up with celebration," says journalist and beer historian Martyn Cornell.
It was only at the very end of the medieval period that hops began to be widely used
There are records of specialty brews being made for weddings, birthdays, harvest festivals, Christmas and other social events. Medieval poetry that references ale frequently associates it with feasting paraphernalia – such as the "ale-benches" described in Beowulf, which could have hosted many revellers.
"One of the things I've come across in the last few years is the idea of the coming-of-age ale," Cornell says. This was brewed on large estates from the early 18th Century. "Very often, when the heir was born to the lord, a hugely strong beer was brewed to be drunk 21 years later at his coming-of-age party," he adds.
This tradition, along with many others, was eventually lost. But it is a good example of how alcohol gained a ceremonial status within the culture.
The mists of time lie thick around the earliest booze once drunk in these islands – whatever it might have been. But the successful marketing of historic ales in the 21st Century suggests we have an innate fascination with our ancestors' drinking habits. As well as Williams' brewery, Innis & Gunn have also tried it, and a handful of Manchester breweries made special edition historic ales for a festival in June 2016.
There is also a growing trend for beers with an aura of being somehow traditional and local, notes Cornell. "Brewers are literally walking into fields near the brewery and pulling out plants, putting them into the beer," he says.
That is just what their ancestors would have done.
Correction: An earlier version of this story referred to the type of analysis done to detect pollen grains as chemical analysis; it is microscopic analysis. It also incorrectly identified an image of meadowsweet; the previous photo has been replaced with the correct one. We regret the errors.
This story is a part of BBC Britain – a series focused on exploring this extraordinary island, one story at a time. Readers outside of the UK can see every BBC Britain story by heading to the Britain homepage; you also can see our latest stories by following us on Facebook and Twitter.