Simon Bird, the boss of the Bristol Port Company has told a committee of MPs that building a barrage across the Severn estuary could be a "killer" to his business.
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The Council is deciding between two locations for the arena. The contractor has suggested work could be cheaper than first thought.
Maisie, who grew up in Saltash, stars in Oscar-winning film The Silent Child.
A 15-year-old girl died in Tavistock on Saturday after apparently taking an unknown substance.