WHEN IS A 'CAMPAIGN' A 'STUNT'?

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The BBC News Website's live coverage has at least mentioned the Taxpayer's Alliance today, but it uses a word that I doubt it would use about the actions of a left-wing campaign group:

15.23 News has reached us of a stunt by campaign group The Taxpayers' Alliance. It plans to travel 1,300 miles around Britain with a giant "debt clock", which will tick over as the government borrows more money. The message, the group says is, "Wake up to the national debt!"