Patriotic Stuart Reeve has been told he could lose his flat - for flying the flag for St George.
Football fan Mr Reeve, of Leahurst Court Road, Brighton, faces court if he does not remove the banner from the back window of his third-floor flat.
The 31-year-old Brighton and Hove Albion supporter branded the demand "political correctness gone mad".
Now he has decided to keep the 3ft by 4ft flag proudly on show in an act of defiance he deems worthy of England's dragon-slaying patron saint.
He said: "I've had the flag since England were in the World Cup four years ago. It used to be on my wall but it fell down.
"About a month or so ago, I was watching television and the sun was coming through the window, reflecting on the screen. I remembered I had the flag, dug it out and used it to block out the light.
"It fitted quite nicely so I left it there but it seems to have stirred up a hornets' nest."
A few days later, Mr Reeve received a letter from Parsons Son & Basley, who manages the block of flats on behalf of the freeholders.
He said: "I was gobsmacked so I just threw it away and didn't do anything about it."
The firm sent him another letter, threatening to put the matter into the hands of its solicitors.
He said: "I rang them up saying, as far as I was concerned, the flag was there to keep the sun out, to commemorate the Queen's Golden Jubilee, because England are going to the World Cup and lastly because St George's Day was coming up.
"I told them if there was anything in my lease which said I could not display a flag I would take it down."
Yesterday, on St George's Day, Mr Reeve received a third letter, repeating the threats of legal action and enclosing a copy of his lease.
This said he was not allowed to fix any notice to the outside of the building or display any placard, sign, notice, board or advertisement anywhere on the premises. Another section said he was not allowed anything likely to cause a "nuisance, annoyance, disturbance or inconvenience, injury or damage" in his flat.
He said: "I couldn't see that any of those sections referred to me having a flag so I decided not to take it down. It has become a matter of principle now."
Mr Reeve, an insurance worker who has owned his purpose-built flat for eight years, said: "I know for some people the England flag has become synonymous with football hooligans and the extreme right wing but to say you cannot display the national flag in your own flat is political correctness gone mad. I have not hung it up as a display of nationalism or of extremism. I think if I had happened to put up another flag, say a Jamaican or African one, no one would have said anything."
Other residents said they were backing Mr Reeve's stance.
Neighbour Veronica Hope said: "I think he was told to take it down because there was some feeling it might have something to do with the National Front, though that was not my opinion."
Fellow resident Mary Phelps said: "Why should he take it down? I certainly don't want him to."
Shula Rich, of the Brighton, Hove and District Leaseholders Association, said Mr Reeve could lose his flat if the freeholder's solicitors proved he had broken the covenants of the lease.
Michael Burrage of managing agent Parsons Son & Basley was unavailable for comment last night.
Mr Reeve added: "I spoke to my girlfriend about it and she has offered to make me a pair of St George's cross curtains. I'm going to take her up on it."
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