The science

On the afternoon of 14 August 1975, as part of a developing thunderstorm across eastern England, the clouds split apart and unleashed a downpour on North London.

The storm was triggered by a combination of a slow-moving low-pressure system, a frontal system near the United Kingdom, a low-pressure system over France, and warm air from the continent.

It had been an exceptionally hot summer that year, with the UK receiving less than half the usual rainfall. But Northwest London just had to be different.

Almost 7 inches (180mm) of rain, around 3 months’ worth, fell in just two hours, the largest daily total recorded in the London area.

However, with water gauges failing due to "damage from debris and being blocked by hail of up to 2cm," according to Smart, real totals were estimated to be in excess of 200mm of rainfall.

Joanna Robinson, weather producer at Sky News, added: "The storm was almost stationary.

"It may have been a 'back building' storm system, sometimes referred to as training cells or training thunderstorms. "

Robinson explained that this is where new storm cells can develop in the place of the original storm, with the downdraught from these new storm clouds establishing and sustaining the whole storm system.

The Weller experience

John Weller, now 58 and a travel writer and photographer, said: “I've been to Bangkok, I've seen the monsoon; it’s nothing compared to this. Nothing. I've never seen anything like it.

“We weren’t scared, just excited; it was an incredible thing.

“It was like being in one of the disaster films I used to love;
I kept expecting Steve McQueen to come swimming by.” 

Unable to cope with the downpour, the Hampstead Heath ponds broke their banks, and water poured down the hill towards Gospel Oak.

At the same time, the subterranean Fleet, Tyburn and Brent Rivers belched forth from the earth, adding their hidden waters to the day’s chaos.

This deluge overwhelmed stormwater sewers and flooded gardens and streets, and Smart stated: "It was a very rare and extreme rainfall."

John Hillaby, writing for the New Scientist in September of 1975, said: “The rain and the hailstones barrelled down; they fell in misty sheets with a noise like boiling fat”

Ex-Lido and Hampstead ponds lifeguard, Tony May, 69, then 19, was walking past the Lido down towards Gordon House Road as the heavens opened.

He said: “It was a waterfall, that whole grass and stairs area in front of the Lido, the water was pouring down towards Gordon House Road.”

John would later become friends with the lifeguard, swapping stories of the Hampstead flooding.

Huddling for shelter, John and April, who saw no sign of the rain stopping, decided to make a break for home on Grafton Road, just half a mile away.

But the weather had other ideas.

With the water reaching their ankles as they passed Gospel Oak station on Mansfield Road, and water sheeting down off the railway bridge, the pair had a "brilliant" idea.

“Let’s wait inside the station and see what happens!”

Unbeknownst to them, torrents of water poured into the underground beneath their feet, causing electrical faults and bringing the Bakerloo and Metropolitan lines to a halt.

Services from King's Cross St Pancras were not back in operation until a week later.

Peter Bergman, then 27, driving home in his Capri to Golders Green from the bookshop he ran in Camden Town, said: “You couldn’t see, it was a fog of rain. It was just thundering down.”

Back in the station, the rising floodwaters had reached the children’s waists, and they were helped onto a low wall in the station by concerned adults.

Sheltering alongside 10 others, the two children watched the waters reach the height of letterboxes and windows. 

April, the older sister, said: “We thought it was fun at first, but then it started to get worrying when the water came up to our ankles, even up on the wall.

“I have never seen water like it in this country, before or since. I have lived in India for many years, and it was on the level of a monsoon.”

Beer barrels, boats and underwater cars

At the Old Oak pub opposite the station, the situation was getting worse by the minute.

Rising floodwaters leaked into the cellar, beer barrels pushed ever skyward and jammed up against the cellar doors.

Reaching bursting point with an almighty crack, the cellar doors split apart, sending beer barrels shooting into the sullen sky, coming down with a plop into the submerged streets.

Bad day for pub owners. Great day for pub-goers.

The barrels floated down the street, past cars that were being pulled under.

Tony said: “Most of the cars were either underwater or semi-underwater. A couple of  VW camper vans were even floating down the road.”

John added: “Cars were floating down the road past us.”

Bergman was in one such car, although half a mile away on Fleet Road, near the Royal Free Hospital.

Peter suddenly saw the sky turn black and the rain come pouring down.

Soon, two and a half feet of water covered the surface of Fleet Road

Peter said: “The car in front of me had stopped, then it began to drift across the road. 

“I learned that day it doesn’t take much to float a car. They’re boats before they sink.

“A fountain of water shot up through my gearbox, and then before I knew it, I was afloat too. Steering made no difference; I was in a boat.”

Worse lay ahead, however. 

Peter added that a new “Lake Hampstead” had formed in the dip in the land around South End Green up towards Hampstead Heath station, with the water “almost 7 feet deep”, according to Bergman.

He said: “There was standing water as far as the eye could see.

“You could just make out a car roof just poking out from above the water line.”

Narrowly avoiding sailing into the lake, Bergman’s new
car-boat drifted sideways, making landfall on Pond Street, and by some miracle, gained enough traction on the waterlogged road to climb the hill to safety.

Road swimmers

Back in Gospel Oak station, occasional swimmers-by crossed the paths of the Weller stragglers, as the skies began to darken.

One of these swimmers may have been Tony May, as he was forced to swim to Queen’s Crescent.

He said: “I was living on Glenhurst Avenue at the time, so I was unaffected, but my friend lived in a basement flat in Queen’s Crescent, so I thought I had better go see how he was.

“I ended up swimming down the Gordon House road, and my friend’s basement was completely flooded.”

Maureen Fisher’s in-laws, Claude and Lily Fisher, lived at 11 Barrington Court, where the flooding came up to 1 metre and destroyed everything on the ground floor.  

Maureen said: “My in-laws were in their 60s, and no help was given to remove all the damaged goods or help to clean up the property. 

“We had to scrub everything down; the floor, walls, doors and up to a metre up the stairs, as well as remove all the furniture.

“They were so traumatised, they just couldn't cope."

Fisher added that her in-laws were insured, but there was no compensation for the loss of personal items, such as wedding photos and birthday cards. 

At around 8 pm, when the rain had finally stopped, the Weller children, whose excitement was wearing off, remembered that their mother was expecting them home.

A kindly gentleman offered to help them get there.

The children were unable to take their usual route through Oak Village due to the newly formed “Lake Gospel Oak”, as John dubbed it, where there were reports of rowing boats ferrying stranded people.

Along with their companion and protector, the children squelched, waded and swam round to Lismore Circus and into Grafton Road and home, taking the longer, safer way round.

As John and April finally came in sight of home, they saw the silhouette of their frantic mother, desperately waiting for their safe return.

Eager hugs were exchanged, and a once-over was carried out to check there was no damage to her offspring.

Then one question rang out from the frightened mother that terrified the children more than any flood water:

“If you could have walked home, why didn’t you do it two bloody hours ago?!”

After making sheepish excuses, the children got dried off and refrained from discussing the event with each other, fearing a vengeful mother’s retribution for her unnecessary worry.