Benjamin Britten, greatest English composer since Purcell.
This is nitpicking really, but 'greatest' according to whom? I'd say that folks like Sullivan, Elgar and Holst (not to mention Vaughan-Williams) are a lot more notable than Britten, and even if you want to restrict your attention to reasonably modern composers, Brian Ferneyhough is more worthy of attention.
'greatest' according to whom?
Decca, some guy writing for the New York Phil, some guy writing for the Daily Telegraph, etc.
Seriously: of course anyone trying to offer an actual careful assessment will say something like "one of the greatest" or "arguably the greatest" or something. As you'll see if you follow all my links above or search the web yourself, one very common practice is to say "widely regarded as the greatest" :-). Personally I rate him well above Sullivan and Holst and roughly equal with Elgar and RVW. I don't ...
Another month, another rationality quotes thread. The rules are: