Possible Clues:

• Membership proof (2 words)
• A school may issue one
• Access requirement, at times
• Item with your name and photo on it
• Driver's license, e.g., in brief
• What a student may swipe
• Bouncers might request this if you're going to music halls perhaps to see bands at The Centre from Dido to Queen
• Proof of membership
• Detective does a twirl in front of Number 10 - presumably, it's revealing who he really is?
• Common proof of age