They were the strange days between an older world and new one, when Charlie Chaplin was knighted and the Sex Pistols played their first gig.

The National Front marched in London, IRA bombs exploded, the Yorkshire Ripper was on the loose and coal miners celebrated a 35% pay rise watched, no doubt, by the new leader of the Conservative Party, Margaret Thatcher.

And in the North Sea, an economic revolution was about to bubble up from the depths of the choppy waters.

The feverish race to extract precious liquid gold from British waters had been played out since the sixties, as exploration companies used increasingly sophisticated technology to pinpoint oilfields which science suggested had to be somewhere.

Finally, in mid-July 1975 – exactly 45 years ago this week – the first of what would become countless billions of barrels of oil was brought ashore.

A trickle at first, before long it would become a torrent; wave after wave of luscious, thick, liquid gold that put the nation on its way to a more affluent future, launched Aberdeen as Europe’s oil capital, and sparked endless debates over whose oil it really was.

Now, however, while a glut of North Sea oil languishes on ocean-going tankers following a collapse in demand and plunging prices, and the sector braces itself for its endgame, the heady days of 1975 feel like a world away.

And it may beg the question of what might have happened if all that oil hadn’t been found?

Pioneering and rival exploration companies had spent years trawling the North Sea for oil when, in September 1969, BP’s semi-submersible rig Sea Quest drilled into what would become the Arbroath field and, a year later, the Forties field.

In an interview given four decades later to mark the Forties’ anniversary, former Sea Quest driller Rob Lingard would tell how he ran to the messroom, grabbed a Colman’s horseradish sauce bottle and snatched the first glug of black liquid gold to emerge from its depths.

“When I think back to that little, tiny rig we had up there compared to the size of them now, we did well,” he recalled.

“We were drilling away and the rig man said ‘2e’ve got some oil on the shakers’. We knew we’d got into oil but we didn’t quite realise how big it was.”

But while BP had pinpointed the UK’s largest oilfield – quickly followed by Shell’s Brent – it would be Denver-based Hamilton Brothers, working on Argyll, 310km southeast of Aberdeen, that would win the race to bring oil ashore.

Using a floating, semi-submersible drilling rig, the Transworld 58, modified to operate as a production platform, oil was pumped onto the 35,000-ton tanker Theogennitor.

Within a week, on June 18, 1975, the then energy minister Tony Benn was on board a hydrofoil at Tower Pier in London, heading down river to BP’s Isle of Grain refinery in the Medway Estuary to greet the tanker and its valuable cargo.

“I hold the future of Britain in my hand,” he declared, clutching a bottle of the tanker’s crude oil aloft, adding that Britain was set to be one of the world’s 10 great oil-producing nations.

Before long, BP would be bringing its own oil ashore.

In November 1975, the Queen pressed a gold button to mark the opening of a pipeline at Cruden Bay which could whisk up to 550,000 barrels of BP oil on a 130-mile journey to the refinery at Grangemouth.

Soon the black river was in full flow. By 1976, Forties field’s four £4 million BP rigs had produced 12.5 million tons of oil and helped ensure Britain was no longer at the mercy of Opec oil prices.

Within a decade, 2.6 million barrels of oil per day were being extracted from 29 North Sea fields across more than 100 installations.

As more companies raced to take out leases to extract oil, terminals were built in Orkney and Shetland. Sullom Voe alone brought work for 500 people while Aberdeen shifted attention from fishing to became Europe’s Klondike.

Family businesses built on cod and herring switched to oil. The most successful, run by Sir Ian Wood, would become a multinational oil services company helping him towards an estimated net worth today of $1.5 billion.

Aberdeen, meanwhile, boomed and losses felt by drifting tourism and cod wars were offset by rich oilmen with very deep pockets.

All of which couldn’t have come at a better time, as traditional industries across the UK collapsed, coal mines and shipyards closed, and car production ground to a halt.

By the mid-80s, the North Sea was providing 10% of the Treasury’s revenues, enabling Conservative government tax cuts, covering the costs of unemployment, and paying off a historic balance of payments problem.

And it provided a cushion for Margaret Thatcher to carry out sweeping industrial reforms while funding a consumer boom when, some argue, the income should instead have been invested in a Norwegian-style oil fund.

While the SNP continued to declare it was Scotland’s oil, the North Sea was, according to Tony Blair in 1987, “utterly essential to Mrs Thatcher’s electoral success”.

Few working offshore would have complained too much. Their 10 days on, five days off routine brought extremely good pay: the average salary within the oil and gas sector in 2012 was £64,000 a year.

But there was also constant danger. In the early days, workers were transported in helicopters without wearing harnesses, puffing on fags as they went. If weather grounded flights, some would be ferried from boats to rigs, clinging on to ropes high above crashing waves.

Concerns that safety was not a high priority seemed validated in 1988 by the Piper Alpha disaster which claimed the lives of 167 men and prompted improved health and safety measures. Helicopter crashes also brought tragedy to the sector.

But still the black gold flowed. By the early 2000s, the Forties field alone had delivered over two billion barrels of oil, while oil gushed from the North Sea at the equivalent of 4.7 million barrels every day, supporting 450,000 jobs across the UK.

No-one can really know what would have happened if we hadn’t found oil on our doorstep; whether we would have been forced to innovate and find new, cleaner methods of providing energy earlier, embraced windfarms and electric vehicles sooner, or limped into economic catastrophe.

However, it’s clear that a sector that is worth around £35bn to the economy, which supports around 300,000 jobs across the UK – 40% of them in Scotland – and has paid £330bn in production tax since the 1970s, is changing.

Ross Dornan, OGUK’s market intelligence manager, said: “The opening of the UK’s first oil pipeline serving the iconic Forties field was a major milestone in our industry’s history and a testament to the importance of North Sea oil to the UK economy which remains the case today.

“The industry has gone on to make a hugely positive impact across the UK – producing more than 45 billion barrels of oil and gas, contributing hundreds of billions of pounds to the UK economy and supporting hundreds of thousands of high value jobs.

“Today, although the industry is facing some of its most difficult challenges, there is still significant potential to be realised from the UK Continental Shelf.

“Our focus is on driving the recovery of our industry so we can make the most of future opportunities including our contribution to delivering energy security and playing a key role in the transition to a low carbon economy.”