Possible Clues:

• Between here and Britain
• W.W. I's so-called 'U-Boat Alley'
• Water to west of Britain
• One end of St. George's Channel
• Part of North Atlantic near Great Britain
• PM concluding I must go first over home counties area, location of controversial border
• Man naturally rises above it
• Man's environment is hard in rough sierra, without river
• Dún Laoghaire's waters
• Hear Isis is choppy body of water