The world of Banksy thrives on secrecy and subterfuge. The anonymous artist put together one of the biggest art shows the city has ever seen, right under our noses, with hardly anyone knowing it was happening.

Here at the Evening Post, we were let into the secret on a rainy Wednesday afternoon in June, days before the show was to be unveiled to the world, when we had a hush-hush visit from two of Banksy's PR people.

The pair giggled excitedly as they sat in the newspaper conference room, explaining to editor Mike Norton, deputy editor Rob Stokes and myself how Banksy wanted his home city's local newspaper to break the story.

At that time, just six people knew about it – including three senior managers at the venue.

The rest of the staff at Bristol's City Museum and Art Gallery were left in the dark about the plans until late on the day before the opening – they were told the museum had shut for two days so a film crew could come in to make a TV programme.

"I think we might have dragged them down to our level rather than being elevated to theirs," Banksy said, referring to the subterfuge employed by museum top brass to keep the event secret from city councillors and trustees.

The Bristol-born artist mounted the elaborate show as a salute to the city which supported his early street art career.

"That meant putting up with a lot of mistakes that were made in public," Banksy said. "But this show was my vision of the future, to which many people will obviously say – 'you should have gone to Specsavers'.

"The international art world had guessed that something was coming for some time," said Councillor Simon Cook, deputy leader of Bristol City Council and cabinet member for culture, sport and capital projects.

"But nobody had any idea where it would be. I think most people assumed it would be in Los Angeles or New York, but for him to bring his work home to Bristol has been a real coup for the city. It is a huge credit to the management at the museum who knew about the show but managed to keep it a secret – even from the city council."

Much of the museum was rearranged to accommodate Banksy's work, with some of the collection taken into storage. Many items from the upstairs galleries remained, to set off Banksy's pieces to best effect.

Rebecca Burton, deputy head of Bristol Museums' collection and archive, said that being one of the few who knew the secret was tough.

"It was an interesting few weeks, while we tried to organise the show without anyone knowing," she says.

"But the amazing thing is we never actually got to meet Banksy – at least we don't think we did. There were a few guys working on the exhibit for the last 36 hours before the show opened, so any of them could have been Banksy. We'll never know which one."

Some of those who were in on the secret didn't even tell their husbands, for fear that the secret would get out.

"I didn't want to be the one who let it slip, so I didn't tell a soul," said Kate Brindley, the former museum director, who left her position on a high with the Banksy exhibition in full swing.

She has been replaced by Paul Barnett, who says that the show has opened up the museum to people who might not normally have visited the attraction.

"The great thing is, the way Banksy interspersed his stuff throughout the building has meant visitors have been encouraged to walk around the whole of the museum," Paul says, "and I think people have been really impressed by the rest of the collection.

"Banksy hasn't just brought his own work here, he's introduced thousands of people to some of the city's rich cultural heritage that they might otherwise never have discovered."

The last 12 weeks have been a voyage of discovery for some of the museum's own staff too – especially for the temporary staff members, who came in especially for the Banksy show.

Tom Scott, 24, of Clifton, started working as a gallery assistant just two days before the exhibition was revealed.

"I had a high-pressured sales job, which I didn't like much, so I packed it in," he says. "I went down to the job centre, and they mentioned this position was available through the summer. So I thought, why not give it a go.

"On my first day I saw all the fossils and minerals and old paintings, and I wasn't sure how I was going to cope with the boredom for the next few months – then all this arrives on the scene. It's been amazing."

But what about the man himself? Did Banksy wander around his own exhibition over the course of the 12 weeks

"He wouldn't have spent a lot of time here during the show," says his PR person Jo Brooks. "He spent quite a while here before the exhibition, putting the finishing touches to the show. But then he made sure he had made his escape before the opening party and media previews.

"Though he did make a few returns to add pieces to the show, or make slight alterations here and there over the summer."

For example, flowers appeared on the ice cream van one morning, then there were the additional pieces that arrived as the show progressed – the suicidal Ronald McDonald perched on an exterior shelf overlooking Park Row, and a portrait of Michael Jackson standing in the door of a Hansel and Gretel-style fairytale house – which was added after the singer's recent death.

"It's constantly evolved as the summer has gone on," Jo says. "That's all been part of it I think. Banksy has kept adding that extra element."

And the response of Banksy himself to all the fuss?

The artist sent a text message to the media assembled for the last day of the exhibition.

"It's nice to see it's been so popular but it makes me a bit suspicious," he said.

"Throughout history all the great artists have been overlooked in their own lifetime and only appreciated once they have gone.

"I'm starting to worry I'm not one of the good guys."