Decades of foreign holidays have left Britons increasingly shaky about details of their own national treasures, according to a survey released today. Almost a fifth are liable to muddle the Pennines with the Pyrenees, guess that Stonehenge was built by the Romans and place Hadrian's Wall overseas, probably in China. Two in five adults think that the bulldog, rather than the lion, is the country's official beast. The gaps in once automatic knowledge have emerged from responses by 3,000 adults to a study marking the launch of an interactive TV series on Britain's best attractions.