'He would be pleased': Family reflects on man's 1971 'Santa' protest to pedestrianise Oxford Street

The married couple were members of the youth wing of the Liberal Party, which in the 1970s was developing a reputation for eye-catching campaigns.

And their concern about traffic in central London led them to an unconventional idea.

"We decided, first of all, to take balloons to London, to take fresh air into the city," she says. "Pollution wasn't talked about a lot then."

Later, along with other campaigners in the newly formed Oxford Street Action Committee, they planned a demonstration which aimed to show Londoners a different vision of the street.

On 18 December 1971, it was the last Saturday before Christmas, and John was celebrating his 28th birthday.

The couple travelled into the West End, but they weren't there to do last-minute Christmas shopping.

On Hyde Park Corner, Lizzie watched as a group of fellow campaigners gathered with armfuls of balloons. Among them was John, who was about to play a starring role.

He would later record the events in a diary, writing: "We all assembled... replete with balloons, one pole-full of which I was carrying while dressed as Father Christmas - a plastic suit purchased at Woolworths."

He added: "The police were present in strength and clearly nervous. We had fly-posted that Oxford Street would be closed at 11am but the poor bobbies had no idea how we hoped to do it."

"Dressed as Santa he was disguised in what looked like an innocent Christmas parade," Helen explains.

Even Lizzie didn't know what was about to happen. "I wasn't told, because they didn't want it to leak out," she says. "They wanted to keep it a surprise."

Nearby, a young woman pushed a pram towards a crossing, carrying what appeared to be a doll. Concealed beneath the blankets, however, was a heavy-duty chain fitted with padlocks.

At exactly 11am, as the traffic lights turned red, the group threw themselves on to the street.

"The girl [with the pram] set off across the road and two heavies grabbed the padlocks and launched themselves at the traffic light poles to lock the chain across the highway," John wrote.

Lizzie says she was "delighted" when the chain suddenly appeared from the pram.

But the attempt lasted only moments.

"Policemen rugby-tackled everyone in sight," John wrote. "The chain was hauled away, the lights went back to green and it was all over."

John was marched to a waiting police bus. "I was to face a charge of obstruction, based on my having waved a pole with balloons attached to the danger of passers-by," he recalled.

He described the charge as something of an "over description," but he didn't contest it and he was fined £2 with an additional £2 in costs.

Lizzie admits the protest was short-lived, but says "the success, I think, came with the amount of publicity we got".

"The publicity that went on about Santa Claus getting arrested at Christmastime was just brilliant."

Lizzie avoided arrest but watched as her husband was taken away. Looking on from outside the police bus, she told a passer-by: "I'd love to go with them but Helen's at home teething."

More than half a century later, the moment still raises a smile.

Helen, who was being looked after by her grandmother during the demonstration, says if her dad was walking down the street today he would be surprised at how much has changed.

"Things have got better in London, with the clean-air tax and electric vehicles, it's just so different. He would be pleased it has been pedestrianised after everything that happened."