On page 4 of the Metro newspaper today (it's distributed free on all the Edinburgh buses, so whatever its faults, the price is right) I read this sentence:
A record number of companies has been formed by Edinburgh University in the past 12 months, taking the total created over the past five years to 184.
A grammar tragedy. It's a verb agreement error. The writer recalls being told sternly that the verb must agree with the head noun of the subject noun phrase, and number seems to be the head noun, so common sense has been thrown to the winds, and the verb has wrongly been put into the singular agreement form—which, of course, is what the simplistic how-to-write books seem to demand.
In this case the correct agreement form happens to be the one that comports with the meaning: the University of Edinburgh has not been forming a number over the past year; it is the companies that have been formed, a record number of them. The singular agreement makes no sense. Lesson: verb agreement is not as mechanical and syntactic as the oversimplified handbook versions would have you believe.
What's going on is actually syntactic, though. Sometimes number is used as an ordinary noun meaning "arithmetical quantity", but like certain other nouns it also has a crypto-quantificational use that involves a kind of bleaching of syntactic potency. In this use, number is transparent to verb agreement: the noun in the of-phrase complement determines the agreement.
Box is an example of a noun that does not normally have this secondary usage: there is typically no number transparency in a box of oranges. It's a singular NP despite the plurality of oranges, so when a box of oranges falls off a truck is grammatical, and *when a box of oranges fall off a truck is not.
But number, in the sequence a number of, is nearly always transparent. We say A number of people are unhappy about it ; the singular agreement form *A number of people is unhappy about it strikes me as plangently ungrammatical.
Analogously, it should be A record number of companies have been formed by Edinburgh University in the past 12 months.
This isn't just an off-hand impression or grumpy peeve. It's a verifiable fact about Standard English. The evidence is overwhelming, positively staggering. A Google search on a number of people feel (a phrase I picked at random) comes up with seven million hits; the phrase *a number of people feels comes up with just seven, and almost all of them show signs of being written by non-native speakers.
The observation is not a new one: the Oxford Dictionaries site gives the correct advice, as I found simply by Google-searching the phrase a number of people are to see what might come up. The Metro journalist didn't think to do any of this to check on normal usage, but just plumped for singular because that's what a number would take.
How could any working journalist or editor be so blind to the natural patterns of their native language?
The question is not just rhetorical; I have an answer to it: nervous cluelessness. I've discussed it here and here among other places. Dogmatic style sheets and don't-do-this books of rules are making people write worse, by making them too nervous to remain securely in touch with their own sense of how their language works. While possibly having good intentions in the first place, books and websites on how to write better are crippling people's ability to write. Professional journalists are putting clearly ungrammatical sentences into newspapers because they think it is required of them by some rule book.
And they daren't even contemplate the idea that in the book they were taught from or bullied into consulting, the rules might be wrongly formulated.
[Post revised slightly for greater clarity, and links added, on 25 and 26 August 2015—GKP.]