A poll commissioned by The Christian Institute found that 11% thought religious liberty had improved under the coalition government, while four in ten disagreed and half of those surveyed were unsure.
The survey, carried out by ComRes, asked for the opinions of those living in the 40 most marginal Conservative and Labour constituencies.
It also found high levels of concern about the constant expansion of equality legislation. Asked whether the "tide of equality legislation has gone too far in elevating equality over religious freedom", just one in five disagreed, while nearly eight in ten agreed or were unsure.
Colin Hart, director of The Christian Institute, commented: "This poll should act as a wake up call to the leaders of the political parties. It clearly shows that in these marginal seats, the key battleground seats where the general election will be won and lost, voters are very concerned about threats to religious liberty and free speech.
"Those surveyed rightly believe that religious freedom in this country has not improved under Mr Cameron's leadership. The government inherited Labour's 2010 Equalities Act which during his premiership has led to high-profile cases which are widely seen as undermining faith. Various court rulings at home and in Europe have been particularly damaging to free speech and religious freedom in this country. Yet instead of amending the law, the government strongly backed the rulings."