A secret garden has been discovered a National Trust site - 300 years after being buried by its heartbroken owner, researchers claim.<br /><br />The 18th Century garden, believed to be 200 metres in length, includes an ornamental pool, Chinese bridge and canal - all preserved in silt.<br /><br />It lies below the site's Great Lake, a main part of the tourist attraction in Stourhead, Wilts.<br /><br />The landscaped was created by the head of one of the country’s richest banking families – and has been lost to history since 1755.