A fifth of British teenagers believe Sir Winston Churchill was a fictional character, while many think Sherlock Holmes, King Arthur and Eleanor Rigby were real, a survey shows.

The canvass of 3,000 under-twenties uncovered an extraordinary paucity of basic historical knowledge that older generations take for granted.

Despite his celebrated military reputation, 47 per cent of respondents dismissed the 12th-century crusading English king Richard the Lionheart as fictional.

More than a quarter (27 per cent) thought Florence Nightingale, the pioneering nurse who coaxed injured soldiers back to health in the Crimean War, was a mythical figure.

In contrast, a series of fictitious characters that have featured in British films and literature over the past few centuries were awarded real-life status.

King Arthur is the mythical figure most commonly mistaken for fact - almost two thirds of teens (65 per cent) believe that he existed and led a round table of knights at Camelot.

Sherlock Holmes, the detective, was so convincingly brought to life in Sir Arthur Conan Doyle's novels, their film versions and television series, that 58 per cent of respondents believe that the sleuth really lived at 221B Baker Street.

Fifty-one per cent of respondents believed that Robin Hood lived in Sherwood Forest, robbing the rich to give to the poor, while 47 per cent believed Eleanor Rigby was a real person rather than a creation of The Beatles.

The study also shows a marked change in how people acquire their historical knowledge these days. More than three-quarters of those polled (77 per cent) admitted they did not read history books, and 61 per cent said that they changed channels rather than watch historical programmes on television.

Paul Moreton, the channel head of UKTV Gold, which commissioned the poll, said that while there was no excuse for demoting real historical figures such as Churchill, the elevation of mythical figures to real life showed the impact good films could have in shaping the public consciousness.

"Stories like Robin Hood are so inspiring that it's not surprising people like to believe these characters truly existed," he said.