People have been warned against exploring a derelict pier head after two teenagers who swam out to the ruin struggled to make it back. The rundown structure has sat abandoned half-a-mile off Herne Bay beach since storm damage in 1978 led to the dismantling of the landmark two years later. Yesterday evening, lifeboat crews were called to reports two boys had not returned to the shore after swimming out to the crumbling eyesore. The pair were found 50 metres off the Neptune Jetty and escorted back to dry land. Lifeboat helm Ruth Oliver said: “They were making their way through the shallow water …