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Those who are still contactable have been unwilling to talk as they fear another crackdown, according to sources.

Every neighbourhood in England and Wales will get a named, contactable police officer, the prime minister is to promise in a major speech.

No further information about the site or the finder was available and Mr Becker was not contactable by telephone.

Bulletin emails and WhatsApp groups allow parents to share information, while their children are traceable and contactable all the time.

Ms Alegre adds that she uses the Freedom app, as opposed to simply turning off her handset, "when I need to be contactable on the phone, but I really don't want to be distracted".