Possible Clues:

• Loss of speech
• Loss of speaking ability
• Inability to use language, after a stroke say
• 'Inability to use language, after a stroke perhaps (7)'
• Inability to use language
• Trouble getting things across has a pair overlooking river worried
• Inability to communicate with a local on the continent
• Difficulty in communication from central Clapham to the continent
• Language problem
• A power is like wizard's (but not magician's) spell: it renders one speechless