Single beneficiaries? What the hell kind of writing is this? A named individual and a political party are not a single entity. Sloppy statements such as this detract from the veracity of the article and the credibility of its author.
Hold your horsies. Whatever the grammatical validity of the construction of the entire phrase (which you don't appear to have properly read), using the subclause "single largest beneficiaries" to refer to two or more persons (each of whom might be an individual, a group of individuals, or an entity) is a common construction that appears in many publications; the author is therefore neither sloppy nor unjustified in using the construction.
For reference:
(1) the google search on the quoted phrase "single largest beneficiaries" - http://www.google.com/#hl=en&source=hp&q=%22single+largest+beneficiaries%22&fp=b8a3d25e1efe4b25
(2) a quotation from the book
The German economy, By E. Owen Smith (Routledge, New York, 1994) at page 414:
"This does not gainsay the gratuitous fillip to domestic growth which the banks, and indeed insurance companies, enjoyed as a result of unification. They were arguably the single largest beneficiaries, ...." (emphasis added). The google books pageview for the quotation cited is
here.
(3) a quotation from a NYTimes article published Dec. 20, 1998:
"The single largest beneficiaries of Mr. Broad's giving last year were Pitzer College in Claremont, Calif., at $1.6 million; Michigan State University, $1 million, and the new Disney Hall concert facility in Los Angeles, also $1 million." (Emphasis added). The article can be found
here.
How's them apples?