The short version: a withheld number is hidden from you on purpose, and UK networks don't offer customers a way to reveal it. That protection exists for good reasons - doctors, refuges and social services withhold their numbers - so the ways to identify a withheld caller go through your provider and the police rather than through a trick.

What doesn't work

  • 1471: it tells you the last caller withheld their number, nothing more.
  • Calling back: there's no number to return the call to.
  • "Unmask" apps: apps that promise to reveal withheld numbers typically rely on diverting your calls through their own service. At best they work unreliably in the UK; at worst they charge a subscription and see all your calls. We don't recommend them.
  • Codes from social media: there's no star or hash code that shows withheld numbers on a UK phone.

What does work

  1. Log the calls. Write down the date and time of each withheld call and anything said.
  2. Contact your provider. Ask for the nuisance or malicious calls team. They can look at calls made to your line, including withheld ones, and may be able to stop them or pass evidence to the police.
  3. Report crimes to the police. Threats, abuse, stalking and persistent calls meant to cause distress can be offences. Call 101, or 999 if you're in immediate danger.

Stop withheld calls in the meantime

  • BT landline: dial 1572 to set up Call Protect and send withheld calls to a junk voicemail.
  • Other landlines: ask your provider about anonymous call rejection, or use a phone with built-in call blocking.
  • iPhone: Silence Unknown Callers sends calls from numbers not in your contacts, including withheld ones, to voicemail.
  • Android: many phones let you block calls from private or unknown numbers in the Phone app's blocked numbers settings.

Is it worth finding out?

Often, no. Most withheld calls are from organisations that withhold by default - hospitals, GP surgeries, the police, some banks - or from spam. If a genuine organisation needs you, they'll leave a message. If the calls are personal and unwanted, the provider-and-police route is the one that can actually end them.

For more detail on police involvement, read can the police trace no caller ID in the UK.