An app to help mobile users avoid nuisance calls and log complaints about dodgy firms has been launched.

Log your mobile number on the free app and you'll appear on the Telephone Preference Service (TPS) – a register of numbers that can't be called by marketeers and other sales firms – and you'll be able to report scam calls made to you.

The TPS Protect app allows you to rank incoming calls for 'trust' on a scale of one to five, which helps users decide whether or not to pick up. Every call that's reported or blocked also helps determine the trust score for that number in future.

The app is run by the Direct Marketing Association – the body behind the TPS – and is available for Apple and Android phones.

How do I sign up?

Download the app, confirm or register your number with the TPS, then you can file complaints about nuisance or scam calls directly. Feedback is passed to the TPS and the Information Commissioner's Office where appropriate.

The TPS is the official opt-out register for consumers wanting to avoid unwanted sales or marketing calls. By law, all organisations including charities, political parties and voluntary organisations can't make calls to numbers on the register unless they have the person's consent. Find out how to protect yourself with our Stop Scams guide.

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How does it work?

The app rates incoming calls with a trust score from one to five – with five the most secure – indicating whether the caller is likely to be a scammer with possible criminal intentions or someone you can trust.

Its functionality is powered by users because every call that's blocked, reported or complained about helps the app create and rank a trust score for that specific number. Users can then see the trust score for incoming calls and look up and file complaints against scam call numbers.

It updates every six minutes, providing protection from new scams if they appear. The app doesn't access your own phone contacts.

If you receive a scam call and want to report it, you copy and paste the number into the box on the screen and it'll show the information the TPS has on that caller. Alternatively, you can post a simple report giving the TPS the number, what the call was about and if you think it was a scam.

New app to help consumers dodge scam callers and file complaints
The new app allows users to screen scam and sales calls and give the numbers a 'trust score'

How much does it cost?

The basic app is a free download though there are extra features users can pay for. Additional subscription features cost 99p a month and allow users to customise call filtering and create 'approved' and 'blocked' caller lists which override all other settings.

For example, users can set a 'personal trust level' from one to five. If they set it to two, all calls with a trust score of one go to voicemail, while other calls ring as normal.

By setting their trust score to five, most unwanted calls will be blocked, but users can still receive calls from specific groups such as charities if they allow that category, while the rest will be diverted to voicemail. If users want to be contacted by one specific charity, they just add that one to their approved list.

Free users continue to receive all calls, but can see the trust score and decide whether or not to take the call.

New users qualify for a free 60-day trial of the paid-for features.