When you gaze over the skyline of any major world city, it’s hard to imagine it all began with a dirty, formerly semi-derelict mill in the north of England.

But the Shrewsbury Flaxmill Maltings is one of Britain’s most important surviving buildings and the grandfather of today’s skyscrapers... even though there’s a good chance you’ve never heard of it.

English Heritage will be opening the newly-restored mill following a £28million refurbishment tomorrow (April 1) – the conservation charity’s first new paid visitor attraction in 21 years.

Opened in 1797, the incredible Flaxmill Maltings was the first building in the world to be constructed using a complete iron frame. The design quite literally changed architectural history, making modern high-rise buildings and skyscrapers possible.

Shropshire was then one of the centres of Britain’s burgeoning Industrial Revolution. The nearby Iron Bridge, which opened in 1881, was the first cast iron structure in the world.

Alongside the factories that followed in its wake, it was also the catalyst for social change via labour reform movements and subsequent legislation to improve working conditions – including the 1833 Factory Act, for which the government received testimony from former workers at the flaxmill outside the Shropshire town of Shrewsbury.

English Heritage’s visitor experience manager for the site, Simon Cranmer, explains: “It is a globally important historic building, just as important as the Iron Bridge and yet virtually no one outside of the local area has ever heard of it.

“Name any famous skyscraper, from the Flat Iron Building, the 22-storey, 285-foot-tall steel-framed triangular building at 175 Fifth Avenue in New York, to the Empire State Building, the Shard and the world’s tallest building, the Burj Khalifa in Dubai, which stands at 2,700ft, and they all owe their origins to the Shrewsbury Flaxmill Maltings.

“Apart from its architectural significance, it casts a light on our country’s industrial past and it is so important that it has been saved from dereliction. It really is a landmark to more than 200 years of industrial history.”

The mill was designed to process flax – used to make linen – at a time of incredible change.

The Industrial Revolution, driven by new steam-powered technology, was rapidly transforming the way people lived and worked – for better and for worse.

As industry transformed towns, the huge building stood out as one of the most technically-advanced of a new generation of factories. Its iron-framed design (which helped make it fireproof) was a true engineering breakthrough, using materials and construction methods not used before.

“I have been able to show with practical certainty that it is not only the oldest existing structure of this type, but is also the first,” Dr A W Skempton, a civil engineer, wrote in 1956.

The mill was home to two different industrial enterprises in its time. First there was flax spinning, for the making of clothes, bedsheets and table linen, and then, when that industry declined with the rise of cotton, it was converted to malt production, where cereals are converted into malt used to brew beer and whisky.

By a striking coincidence, each very different production era lasted for 90 years. During the flax years, the mill buzzed with the noise of spinning machines and hundreds of workers, men, women and children, mostly toiling at the machines for 12 to 14 hours a day, sometimes six days a week.

Simon said: “It was a good time and a bad time. Obviously children were working here in very difficult and dangerous conditions.”

The new exhibition asks visitors to think about whether this was right and also poses questions about the garment industry around the world today with conditions as bad as ever for young Third World workers producing clothes for fast fashion.

In contrast to the flax years, during the maltings era just a few dozen men worked at the mill, moving tonnes of barley through the malting process, often by hand.

In the 1790s, Shrewsbury was already a prosperous commercial centre and a busy border town connecting England and Wales. It had established transport links and the new Shrewsbury Canal, which was nearing completion, making it easier to move finished goods and raw materials.

Businessmen Thomas and Benjamin Benyon and John Marshall lived in Leeds, where they already had two mills but one had burnt down.

The Benyon Brothers were originally from Shrewsbury, and Benjamin wanted to move back and establish a new modern mill. To that end, they enlisted the help of Charles Bage to design a groundbreaking new mill building.

This was Bage’s first commission and prior to this he had been working as a surveyor and wine merchant. In the early days of the industrial revolution, mills making textiles often burned down. The combination of timber-framed buildings, flammable materials, and working by candlelight was often disastrous.

Marshall and the Benyon brothers had first-hand experience of mill fires, losing a mill in Leeds in 1795, just two years before setting up in Shrewsbury. Coming up with the right design took careful thought.

Bage exchanged letters and ideas with William Strutt, a mill owner in Derbyshire, who was experimenting with fireproof construction.

Strutt had built a mill with iron columns supporting timber beams, which in turn supported a vaulted brick ceiling. Bage took Strutt's approach even further, replacing the timbers with iron beams. This would greatly reduce the risk of fire.

However, the iron frame that made the mill fireproof had an unforeseen consequence: a metal frame makes it possible to build higher and higher.

The Main Mill was the first iron-framed building in the world. Seen from outside, the new mill looked like any other of the time. It was the iron frame on the inside that made it so innovative.

By using iron where traditional buildings used wood, Bage made sure fire could not spread from floor to floor. Rows of cast-iron columns support the beams, which in turn support arched brick ceilings. The parts slotted together and were secured with metal nuts, bolts and wrought iron tie rods in a neat, systematic way, much like a giant Meccano set.

Constructing this pioneering flax mill took just two years to complete. It was a masterpiece of local craftsmanship. The pieces of the complex cast iron frame were transported by horse and cart from William Hazledine's foundry, just over a mile away, in Coleham to the site and constructed at the same time as the brick walls were being built. Each one of the thousands of bricks was made by hand.

It was a soaring success but when, in 1887, after almost a century of production, the flax operation closed, the machinery and most of the other contents were auctioned off.

During the Second World War when the malting side of the business was temporarily halted, the buildings here were used as a barracks for recruits training as infantrymen.

After the war in 1948, Ansells, the Birmingham brewing company, bought it and a new productive chapter began. Eventually the technology at the maltings was out of date, overtaken by huge purpose-built facilities and the last malt was made in 1987 – 101 years after the Marshall’s business made its last thread.

Simon picks up the story: “After it closed as a maltings in 1987 the building fell into disrepair and was in real danger of falling down. It became derelict and vandalised and was broken into on numerous occasions and the police called. It had become an eyesore and its future was in jeopardy.”

In 2005, Historic England bought the site and in partnership with the local council, and thanks to a £20million National Lottery Heritage Fund award, the biggest ever of its kind, plus some initial funding from the European Regional Development Fund, the site was saved.

Now Historic England is handing over the running of the visitor attraction to English Heritage. English Heritage members can visit for free and it is hoped the site becomes a major tourist attraction not just for the local area but for national and international visitors too in the way Iron Bridge is.

The attraction is made up of eight buildings each with a unique story to tell, including the 1797 Main Mill, "the grandparent of skyscrapers.”

The site also has four floors of office rental and there are plans to build around 100 homes at the front with ground-breaking due to take place in 2027.

Simon adds: “If this site had been knocked down and redeveloped, it would have used five times the amount of carbon. By restoring the building and regenerating the whole site it is not only ecologically sound by using an old building, it reinvigorates the whole town and boosts Shropshire’s burgeoning tourist economy.

“It is a really pretty county that looks very different to how it did then but this is the birthplace of Britain’s industrial revolution and that is something to be proud of and for future generations to understand.”

Matt Thompson, Interim Curatorial Director of English Heritage, adds: “As with much of England’s industrial heritage, Shrewsbury Flaxmill Maltings is a hugely under-appreciated historic site. It is a superb example of living, breathing heritage.”