Ken Livingstone is keeping out of the row about whether the city where he has a second home should have an elected mayor.
Last year the former Greater London Council leader was chosen by the capital as its first directly-elected mayor.
On October 18, Brighton and Hove will hold its referendum on whether it too should have an directly-elected mayor.
Both the Yes and the No campaigns were anxious to secure backing from Mr Livingstone, who has a weekend home near Brighton station.
For the Yes campaign, Lord Bassam of Brighton said in a secret document leaked to The Argus that efforts would be made to gain Mr Livingstone's support.
But the London mayor has told the No campaign he will not be supporting either side.
Labour councillor Jack Hazelgrove, treasurer of the cross-party Allies for Democracy group, said: "I'm not surprised that Mr Livingstone is refusing to back the campaign for a new kind of mayor.
"After all, he campaigned quite vociferously against the idea of having a mayor for London in the first place. It was only after the decision to go ahead with the idea that he decided to stand."
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