One of Banksy's best-loved Bristol murals has been targeted by vandals as fans continue to arrive in their droves for his exhibition just up the road.

The Park Street image shows a naked man hanging out of a window as a suspicious husband peers out of the window into the distance as his scantily-clad wife stands behind him.

In 2006 the city council asked the public whether they wanted the mural to stay or go - 93 per cent of respondents asked for it to remain.

But the famous image, which is loved by tourists and residents alike, was splattered with blue paint sometime on Monday night or in the early hours of Tuesday.

Today Bristol City Council took a sample of the paint to establish whether it was going to damage the mural and tomorrow it is expected to be carefully cleaned.

The attack comes 10 days after the anonymous artist opened Banksy Versus Bristol Museum on the Triangle which has seen thousands of people queuing over an hour to see.

In April red paint was splattered across Banksy's Mild, Mild West art work in Stokes Croft.

The mural was painstakingly repaired by the People's Republic of Stokes Croft, which is in favour of street art. Anti-graffiti group Appropriate Media claimed responsibility.

The group have not as yet claimed responsibility for the attack at Park Street.

Councillor Gary Hopkins, of Bristol City Council, said: "I'm disappointed but unfortunately not surprised. People are built up and then there are always some people who want to drag them back down again. I think the turning point in his reputation was when we decided to keep this piece of work but maybe that destroyed his street cred."

Mr Hopkins said that Tory councillor Albert Murphy had agreed to repair the Banksy for free.

He added: "Clearly this work is a tourist attraction and now that it has been damaged we must do what we can to restore it. We must be careful to examine what paint it is and whether it is going to be easy to remove without damaging the mural underneath.

"That of course is a great concern because it would be a great pity as a lot of people from around the world come and see it and find it amusing as well as those living in the city.

"I think this attack is basically by people who think that Banksy has become part of the establishment but I think there is a difference between Banksy who produces work that people can enjoy and base taggers who want to steal public space. I would not call them artists.

"But with Banksy, as a city, we have effectively given his work retrospective planning permission. Maybe he will go back and touch it up - you never know."

Cllr Murphy said: "I am going to get a sample of the paint and get a break down of the constituents to see if it will affect the Banksy.

"I am not anti Banksy, I am anti graffiti. Now that someone has chucked paint all over the Banksy it's now graffiti so I am gong to sort it out.

"At the moment it's a case of seeing what the paint is and then getting somebody to clean it as carefully as possible."