Related Clues:

• Temporary stone work at break in wall, say
• His castle may be seen at Alnwick
• A medical man tours hospital for a specific purpose
• Military assistant's taken over house for specific occasion
• Impromptu remark
• A GP touring hospital for a purpose
• Speak without planning or preparation
• Hospital's brought in a medic for a special operation
• Spontaneous remark from head librarian
• For one purpose only
• Hospital covered by a physician not in general practice
• Unplanned, unrehearsed
• Formed just for a single purpose
• Stevenson, lacking a book, improvised
• Make an impromptu speech