Banksy fans are spending more and more time walking around the exhibition in Bristol – leaving people queuing outside with more than a three-hour wait.

Bristol City Council says each day visitors are spending longer inside the City Museum & Art Gallery, which has also meant fewer people are being admitted each day.

While an average of 4,700 people were being admitted to the museum every day in the first few weeks of the graffiti artist's show, which opened in June, an average of only 3,500 visitors are now making it inside.

Bristol City Council spokeswoman Helen Hewitt said the idea of placing a time limit on tickets had been ruled out before the exhibition was opened on June 13.

Almost 250,000 people have visited the free Banksy vs Bristol Museum exhibition and nearly 300,000 people will have seen it by the time it closes at the end of the month.

Ms Hewitt said: "People are staying in the museum longer and we can only have a certain number of people in the museum at one time.

"When the exhibition first opened, people were spending an average of 40 minutes in the museum but now people are waiting longer and making much more of a day of it when they get in.

"I spoke to someone recently who said they had spent four hours in there."

Last week, the Evening Post revealed that elusive Bristol-born graffiti artist Banksy was paid £1 by Bristol City Council for staging his exhibition in the museum.

A contract drawn up between a company representing the graffiti artist and the city council has been released after a request under the Freedom of Information Act.

It also insists the museum destroy all CCTV footage that might have captured the artist install, view or remove the exhibits 30 days after it was shot.

The document, published online, also commits the museum to cooperating with "the creation by the artist of a book about the exhibition".

At the beginning of the month, the city council announced that the exhibition would open for four late nights until 8pm to cater for demand.