Keep Britain Tidy said 52 per cent of daily smokers professed not to see a problem with getting rid of their cigarette ends in this way, with just over half realising that the debris would finish up in the sea.
The survey of 4,146 people, including 502 smokers, was carried out to raise awareness of the link between cigarettes and the marine environment.
Allison Ogden-Newton, chief executive of Keep Britain Tidy, said: “We wanted to show how simple everyday behaviour can affect the environment.
“While flicking a cigarette down the drain may not seem harmful, we need to ensure smokers understand that this has a direct and often drastic impact on wildlife.
“We need to challenge this view that discarding cigarettes in this way is acceptable and get the message to smokers that this is still littering.
“We hope that this research will further educate the public about the effects of smoking-related litter.”
Concern for the oceans was raised by Sir David Attenborough in the BBC’s Blue Plant II series.
Keep Britain Tidy and Sea Life Manchester will launch an installation today with three giant cigarette butts to show the effects of discarding such litter.