A teenager has been arrested after a mass bomb hoax closed hundreds of schools across the UK.

The National Crime Agency (NCA) said there was “no credible threat to the emails” received this week.

A 19-year-old man was arrested by Hertfordshire police in Watford on Wednesday evening on suspicion of blackmail and making malicious communications.

The NCA said in a statement: “We understand parents’ and teachers’ concerns but stress there was no credible threat to the emails schools received.

“However we are taking the communications extremely seriously.

“As this is a live investigation we are unable to comment further.”