Speaking outside the Old Bailey, Jenny Hopkins, of the Crown Prosecution Service, said Thompson put scores of lives in danger by starting the Croydon blaze, including both firefighters and those living nearby.
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The popular game relies on Google Maps, a problem in South Korea as those functions are limited by the government.
A Met Office warning covering much of England and south-east Wales is expected to remain in place until 11am.
A band of cloud and patchy rain is expected across Scotland and Northern Ireland, moving southeast as the day progresses.