Is it acceptable to use a single hyphen as a dash (as the BBC does)?

Is it acceptable to use a single hyphen as a dash (as the BBC does)?

Example from BBC News:

Venezuela - a major oil producer - has been heavily affected by the fall in oil prices on international markets.

Like many institutions in the UK, the BBC has published its entire style guide online. The style guide is massive and detailed and is the result of hundreds of combined years of writing and editorial experience. Like other major style guides, we can assume that each rule is well-considered, and since all style guides change, we know that rules are often reconsidered.

Before looking at the BBC's rules, let us talk briefly talk about American English and its use of hyphens and dashes. The post pointed to by @tchrist is an incredibly concise and clear explanation of American usage of hyphens and dashes. (Although, it does not explicitly mention not to use spaces.) I have not read an American style guide that dissented on this topic.

The BBC is British, however, so it is possible that they view dashes the way they view colours. In looking through the style guide, I am quite surprised that I could not find any discussion of en-dash or em-dash. In fact, the guide seems quite comfortable interchanging the word hyphen with dash.

All of the relevant pages I could find:

1. An extensive discussion of hyphens that exactly matches hyphen usage in American English.
2. A brief mention that a "dash" (of unspecified kind) can substitute for a comma. But the example given is what Americans would call a hyphen, "I heard a voice telling me ‘Come home’ - Ronnie Biggs".
3. Three different pages stating, "Note that tiebreak scores are inside brackets and separated by dashes." (emphasis added.) But the accompanying example text clearly uses hyphens without spaces. "6-4 6-7 (2-7) 7-6 (7-4)" Pages 1, 2, and 3.

Conclusion: if you are writing for the BBC, your example is required; if you are writing using American style guidelines, then the example you provided is absolutely wrong; and if you are writing using British style guidelines, then I would look for more authorities on the topic.

Generally speaking there's little difference between British and American use of dashes, at least as compared to hyphens. The use of a hyphen character (or technically hyphen-minus) made sense in legacy (pre-unicode) systems as the dashes weren't always available and were encoded at different code points in different systems. That hasn't been a good excuse for some time though.

Is possible they're spaced En-dashes but I assume you've checked. http://en.m.wikipedia.org/wiki/Dash says that spaced En-dashes and unspaced Em-dashes may both be used as parenthetical dashes.

Using multiple hyphens as a substitute for dashes is useful for avoiding ambiguity but shouldn't be expected in web or print output. It's how LaTeX for example inputs dashes and so you'll see it in text formats -- including here.