Last year, Australia approved similar laws to those proposed by Health Secretary Andrew Lansley, introducing plain packaging to reduce the attractions of smoking. Three global tobacco giants launched lawsuits saying the rules infringed trademark rights.
Three of the world's four largest tobacco groups, Philip Morris International, British American Tobacco and Imperial Tobacco are challenging the new law in the High Court.
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The royal couple have been in the US to mark the 300th anniversary of the foundings of New Orleans and San Antonio.
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