Doesn't mean BBC coverage is 4.6 times better, but I know you're not saying that. So the race garnered 5.6 million viewers, I think that's a more interesting stat, considering there appeared to be about 80-90% of the tickets sold.
http://www.f1revs.com/2012/05/bbc-sky-spanish-gp-viewing-figures.html
http://www.f1revs.com/2012/05/bbc-sky-spanish-gp-viewing-figures.html