Politicians in Salford have said more needs to be done to drive racism from communities after a graffiti attack on the home of a 10-year-old boy and his father – and before a rally by the anti-Islam activist Tommy Robinson is due to take place in the city.

In a joint statement, the Salford and Eccles Labour MP, Rebecca Long-Bailey, and Salford’s mayor, Paul Dennett, condemned the “sickening” racist message “no blacks” sprayed on the front door of Jackson Yamba and his son, David, just days after they moved in this month.

“This appalling attack on members of our community represents an unwelcome reminder that racism is still prevalent in our society today,” they said, adding that there was “still a lot of work to be done to drive racism, in all its forms, from our much loved city and society in general”.

Greater Manchester police launched a hate crime investigation into the graffiti that appeared on the home of Yamba, 38, and his son five days after they moved in on 3 February. No arrests have been made so far.

Racist graffiti daubed on the doors of the Salford flat of Jackson Yamba and his son David, 10. Photograph: Christopher Thomond/The Guardian

Long-Bailey and Dennett said Salford had a proud legacy of multiculturalism and a long history of welcoming people from all over the world.

They released the joint statement a few days before a planned demonstration by Robinson and his supporters outside the BBC’s headquarters at MediaCity, Salford, on Saturday.

Robinson, whose real name is Stephen Yaxley-Lennon, is planning to show undercover recordings of the BBC journalist John Sweeney who was making a film about the English Defence League founder.

They said: “In recent demonstrations held by ‘Tommy Robinson’, former members of the National Front, Combat 18, and other fascist groups have attended and have attacked anti-racist protesters whilst shouting anti-Muslim and antisemitic chants.

“Robinson has also aligned himself with the mainstream right, since being hired as an adviser to Ukip under Gerard Batten’s leadership. A move which ‘appalled’ even Nigel Farage.

“We have a rich and diverse community here in Salford. We oppose antisemitism, Islamophobia and all forms of racism. These attacks and rallies have no place in Salford and we will fight to drive hate and racism from our communities here in Salford, and across the UK.”