Possible Clues:

• It hinders advance
• Block to progress
• "Let" — for the first lob ace's sent out
• Something to be negotiated
• Let jazzmen into joint, mostly, on reflection
• Bar's bottle opener drunk locates outside
• No new constable can resolve hold-up
• One may be on course for negotiation
• Cable's to broadcast rock
• A stumbling block to Basle, disunited about a century