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In fact there were only five people who knew the plan, one of them David Cameron, the Prime Minister, and the only proper rehearsal had taken place in the dead of night.

Mr Heatherwick, 42, was appointed to create the cauldron, the centrepiece of every Olympic opening ceremony since 1936, two years ago.

His other designs include the replacement for London’s Routemasters and the East Beach Cafe in Littlehampton.

Since his appointment he was been sworn to tell only those who need to know and yesterday was relieved to describe his creation fully.

“It is great to have the opportunity to actually talk about this big secret we had to keep for two years,” he said.

“When we were thinking about the cauldron , we were aware that cauldrons had been getting bigger, higher, fatter as each Olympics has happened and we felt we should not try to be even bigger than the last ones.

“It didn’t feel enough to just design a different shape of bowl on a stick so we were trying to rethink it fundamentally — this idea of having no cauldron and instead each country would bring together an object — no bigger than a few bits of paper — and that these children would carry these polished copper objects.”

The cauldron is made up of the “polished copper objects” which are in the shape of flower petals about a foot long.

There are 204 of them, representing each of the countries taking part in the Olympics, and they are attached to steel pipes, each of them about 28 feet high, which contain a gas pipe connected to the mains supply.

The pipes are made of a special type of steel with a heat and acid chemical treatment that give them a colour called ‘bad black’. Each petal is individually made and each had to be clicked into place into a specific rod. At the end of the Games the cauldron will be dismantled and the petals scattered to the 204 nations that took part in the opening ceremony.

The time it took the athletes to come into the stadium — almost two hours — gave the cauldron team time to assemble the complex structure.

The cauldron was actually kept beneath a black cloth and hidden from view and beneath the stage. The petals were taken from each team and without anybody seeing taken below the stage to the cauldron where they were attached to the pipes out of sight of the crowd. When the process was completed, the cauldron, with the pipes at that stage still flat, was raised to the level of the stage but still kept under cloth. Only when the cloth was removed, did the cauldron appear.

There was a further technical difficulty in lighting the petals. Each contained an igniter within it and the team tested several different ways if getting the cauldron lit.

“In the end, each athlete lit a petal and that petal would light the next one and the flame would go around the ring,” said Mr Heatherwick.

“We had 45 seconds and each of these seven athletes had that time to do it before the whole cauldron became lit.”

It took the seven young athletes 45 seconds to light the flames and then a further 45 seconds for the cauldron to be raised. The inner ring is raised first followed by nine outer rings so that in the time it takes for the first ring to become vertical, the final one is just lifting into the air.

“Each of these petals was unique. We drew each one,” Mr Heatherwick said.

“The 204 petals were arranged in ten rings, the inner ring lifted first and the next ring and the next one. When the first ring became fully vertical, the last ring was just lifting. It was like a dandelion with the seeds that you blow. It was technically very difficult to make it work. When it worked last night, it was a huge relief.”

The design work started two years ago and the construction, which took two months, was carried out by Stage One, a metalworking firm based in Towkwith, North Yorks, which is one of the few companies in Britain with the expertise for the task. It is also behind the giant Olympic rings which have been suspended from Tower Bridge over the River Thames and has previously worked on the Athens Olympics opening ceremony and the Winter Olympics in Canada.

The team tried it out first at the manufacturers before bringing the cauldron to London for secret testing that took place at 3am when all the volunteers had left the stadium and when no helicopters could fly overhead.

“Part of the problem was how to keep this secret from the many thousands of volunteers who were all helping with the opening,” he said.

“We brought it to the stadium in pieces and when everybody had gone home and no helicopters were flying at three in the morning only four or five of us were in the stadium and we tried to make it work.”

After the triumph early on Saturday morning, there is some degree of disappointment that the cauldron will be invisible outside the stadium.

Yesterday workers start the process of moving it to its permanent place at the corner of the stadium occupied by the giant bell which started the Opening Ceremony.

The cauldron sits on a base and when it is moved, the flame will be transferred , the gas disconnected and the cauldron relocated to the spot where the bell is.

After the closing ceremony, it will be no more.

“The idea then was that at the end of the Games the cauldron will be dismantled and will be radiated back to the countries that brought them in, by which time all there will be all these highly scorched elements and everybody gets a piece,” he said.