In a sign that Washington may be one of the first states to buck the trend on equal marriage referenda, a new poll suggests that voters in the state might approve the measure during the presidential elections this November.

Washington legalised equal marriage early this year, but opponents had gathered more than double the required number of signatures to put the issue to voters through a referendum. The referendum will also ask the voters whether smoking marijuana should be legalised.

Every state which has had a referendum on equal marriage so far has moved to reject it, including, most notoriously, California through the Proposition 8.

However, according to a left-leaning think-tank, Public Policy Polling, voters in Washington are set to approve equal marriage, as they would the use of marijuana, the first time for the state in history.

Nearly 51% supported equal marriage, with 42% opposed, while the rest remain undecided. On marijuana, the votes split 50 to 37 in favour. The error margins are roughly plus or minus 3%. Among democrats in the state, the support for equal marriage jumped to 82%.

Recent polls have found that more Americans support equal marriage than oppose it, a reversal of the historic trend that first began to be observed a year and a half ago.