Possible Clues:

• Many sentries become radio enthusiasts
• They have an inclination to sneer when they make use of 27 across
• They're at the radio, not the TV (9)
• Is that what they do? Hear, hear!
• A catalogue of sneer that they get by ear
• Performers of tap dancing set to board ships
• They're all for radio, not TV
• They can't get a radio but see TV (9)
• Lean to one side and sneer, agitating the audience
• The crooked set in the liners are all for radio