The Guardian offers an API as deep and robust as the New York Times Article API when it comes to content analysis.
The Guardian's API offers more than "1.7 million pieces of content", with published items as far back as 1999. You can register as a developer here, which gets you 5,000 API hits a day and an API key that looks something like this:
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The Guardian has a handy interactive explorer to interactively tweak the query parameters.