A "Happy Brexit Day" sign posted on a door in a block of flats has sparked outrage after telling people to "speak the Queen's English or go home".
The demand was pinned to a front door in council-owned Winchester Tower in Norwich as the UK officially left the EU on January 31.
The anonymous writer hails "we finally have our country back" and slams immigrants which it claims have "infected this once great island".
A photo of the letter was shared widely on Twitter as people dubbed it a hate crime.
It orders non-native English speakers to "obey the rule of the majority or leave".
"If you do want to speak whatever is the mother tongue of the country you came from then we suggest you return to that place and return your flat to the council so they can let British people live here and we can return to what was normality (sic)," it reads.
After the letter went viral, a neighbour of Winchester Tower told the Eastern Daily Press: "The bottom line is I am a Christian and I believe you should love your neighbour, wherever they are from and whatever colour their skin is.
"It is quite surprising because I have always felt that there's a good community feel in this building and I can't think of anybody here who would have written such things."
Norwich City Council has condemned the letter, which has now been taken down, and reported it to police.
In a tweet, the council said: "You may have seen a photo of a poster that has appeared in one of our properties. Norwich has a proud history of being a welcoming city, and we will not tolerate this behaviour.
As soon as we became aware of this incident, we reported it to Norfolk Police and they are investigating. We take this very seriously and encourage residents to contact us or the police if they have any concerns."
A Norfolk Constabulary Police spokeswoman said: “Officers attended Winchester Tower last night and all posters had been removed. Those posters kept by residents have since been seized for forensic enquiries and we will be working with the council to examine any available CCTV.
“There is no place in society for hatred and intolerance. Nobody should have to face intimidation because of who they are and it is more important than ever that we stand together in the face of hostility.
"We remain committed to helping people feel safe and secure as they go about their lives.
“The matter is being dealt with as a racially aggravated public order incident and anyone with information which could help officers with enquiries should contact Norfolk Police on 101 quoting crime reference 36/7964/20.”