Possible Clues:

• A matter of course, or part of a pound
• 27 across might be going around with a twisted tail
• Said to bypass Belgium, it is a kind of motorway
• Going round - the M25?
• Not much spoken about, as space travel can be
• Going round part of the mouth externally
• The M 25, say - what's said about small section?
• Bristol centre overlooked taking a turn going round city
• Descriptive of the M25
• Rob tail (anag.)