Nearly three-quarters of the public believe that the war in Afghanistan is unwinnable.
The figure has grown from 60% in June last year to 73%, while more than half (55%) think British troops should be withdrawn immediately compared to 48% previously.
Nearly half of those questioned (46%) have no idea why we are in Afghanistan and do not understand why British soldiers are fighting, up from 39% before, the latest Index poll results conducted by ComRes found.
They showed that public understanding of the purpose of Britain's mission in the conflict has fallen from 44% last October to 38% this week, and now nearly half (48%) of those asked do not believe they have a good understanding of the purpose of Britain's mission there.
Just 18% think that having forces in Afghanistan makes Britain a safer place with three in five who disagree (60%).
Meanwhile more than half (55%) believe that the threat of terrorism on British soil is increased by British forces remaining in Afghanistan.
One in five (21%) disagree with this while one in four (24%) do not know.
More than half (57%) disagree that the deaths of British soldiers in Afghanistan are justified by the cause they are fighting for, rising from 50% last June. Now just one in four (26%) agree and 17% say they are not sure.
The survey involved 2,062 adults being questioned online between last Friday and Sunday and was broadcast on ITV1's News at Ten last night.