For some it is simply an eyesore, but for others graffiti has as much worth as an old master. In Bristol, reputed home of Banksy, the street artist who has done more than any other to elevate graffiti off concrete walls and into galleries, the question is to be settled by the public.

Bristol city council is planning to let the public vote before murals on buildings, walls and fences are scrubbed clean or painted over. If citizens decide they like it, the work will remain.

The move comes as the "Banksy v Bristol Museum" exhibition in the city closedtoday having attracted more than 300,000 visitors since June. Queues for admission were up to six hours long over the Bank Holiday weekend.

As part of its formal street-art policy "to seek to define and support the display of public art", the council is pledging "where people tell us that murals or artworks make a positive contribution to the local environment, and where the property owner has raised no objection" the graffiti will not be removed.

Photographs will be posted on the council's website and the public asked to voice their opinions.

The policy was created after a Banksy work, showing a naked man hanging out of a window while his lover's partner looks for him, appeared on a council-owned building in 2005, sparking debate over whether it should be removed.

The council set up an online poll, with 93% of those voting saying they wanted to keep it.

"We have said informally that if it is street art that people like we will keep it but we want to formalise it now into a policy," said councillor Gary Hopkins, cabinet member for Environment and Community Safety.

"People want us to keep up the war against the taggers so we have had to work out a way to differentiate between the taggers and the artists".

Predictably, fine-art aficionados loathe the idea. "The two words 'graffiti' and 'art' should never be put together," said the art critic Brian Sewell. He added the council were "bonkers". "The public doesn't know good from bad."

"For this city to be guided by the opinion of people who don't know anything about art is lunacy. It doesn't matter if they [the public] like it. It will result in a proliferation of entirely random decoration, for want of a better word," he said

"Buildings of fine quality, and there are many in Bristol, will be defaced. The architecture must take primacy over whatever street artists may want to do."

Bristol city council faced embarrassment in 2007 when its workers painted over a Banksy mural estimated to be worth £100,000, causing public outrage. Since then it has ordered all Banksy work to be preserved.

"A couple of pieces of art have been scrubbed off in error, but staff now know if it is a really good piece of art work they refer it on," said Cllr Hopkins. "Street art is part of Bristol and people have complained about Banksy in the past. But I think public opinion has shifted."

He said of those the Banksy exhibition has attracted, 70% were from outside the city, "so street art has generated masses of money for Bristol".

"Some people feel threatened by tags, so we have commissioned murals to give a positive image and that does prevent graffiti. We also get the kids that have been involved in illegal tagging and get the artist to train them."

The exhibition, for which the museum paid just £1 and which was free to the public, was kept secret until the day before it opened. Featuring 100 works including his trademark stencil paintings, animatronics and installations, organisers were forced to introduce late-night openings to keep up with visitor numbers.

"It has been such an amazing experience, I can't believe how great the turnout has been," said Helen Hewitt, council spokeswoman. It has seen as many visitors in its 16-week run as the museum normally attracts in a year.

But for Sewell, the exhibition's popularity was another sign that "the art world has gone absolutely crazy".

"Any fool who can put paint on canvas or turn a cardboard box into a sculpture is lauded. Banksy should have been put down at birth. It's no good as art, drawing or painting. His work has no virtue. It's merely the sheer scale of his impudence that has given him so much publicity."