I think most would agree that any modern English variant, from anywhere in the world, is very, very different from Old English. However, I would say American English is more similar to Old English in some respects than modern British English is.
The most striking way, in my mind, is the stronger retention of the 'r' sound. I have heard (from a professor speaking on the radio; I don't have a citation) that American English generally sounds more like Old English than British English does. (In my oversimplified way of thinking, spelling has changed slower than pronunciation, and American pronunciation generally seems to stick closer to a "naive" interpretation of the letters than British.)
In other ways, of course British English is more like Old English than American is.
While not credentialed, here is a nice discussion on the topic: Which accent is more similar to that of the old English?
American English is a living language spoken and written by millions of people in the year 2014, that continues to evolve.
British English is a living language spoken and written by millions of people in the year 2014, that continues to evolve.
Both have features and vocabulary that the other once had and since lost (or at least which is now less commonly found in it).
Both have innovations that the other has not adopted as eagerly.
Describing either as archaic or modern compared to the other is meaningless (now Yola for example, is a form of English that is genuinely not modern).
It could certainly make sense to describe one as more innovative in a particular regard, but in actually examining the two we find that the two seem to keep apace for the most part.
There's perhaps more spellings that differ from how they were in 1801, due to Webster's reforms being more heavily adopted in the US than the UK, however:
- Many of these were a matter of him settling on one of two or more forms found in both the US and the UK, so in these cases neither is necessarily the more modern.
- Many were adopted in the UK too.
- Many were not adopted in the US.
- There were spelling innovations in Britain such as beginning to favour -isation over -ization.
We find verbs changing forms more strongly in one than the other, but it will sometimes be British English that is the innovator, sometimes American.
We find many neologisms in American English, but also some relics like teamster being used long after any teamster dealt with horses.
A great many differences relate to concepts or inventions that are themselves relatively recent, and hence the term for either is equally recent in both.
A lot of terms have come into one of these countries from its immigrant populations and its imperial adventures, but different terms have come into the other from its different immigrant populations and different imperial adventures; while US soldiers may have become "gung ho" later than than for UK soldiers missed "blighty", there isn't really much justification calling one more of an innovation than the other.
Really, while one could spend time producing a thorough score card and argue one way or the other on the basis of it, in any meaningful sense they're both about equally modern.
Best Answer
This is a matter of style, so it's not possible to give a definitive answer on what the correct use is. Different style guides, and different people, will use dashes in different ways.
Having said that, it's generally been the case that more British style guides will say to not use an em dash but, where US style would use an em dash, to use an en dash that's surrounded by spaces.
From the University of Oxford Style Guide (PDF), page 13:
Note that the guidance here to not use the em dash goes against the guidance of most US-based style guides. (But also note that the use of the en dash recommended in the last two categories—without a surrounding space—does match the use of the en dash recommended by most US style guides.)
But that is only one of the common style guides used in the UK—and many companies and people in the UK do use em dashes. So, it should not be thought of as definitive. As with other aspects of style, pick the style guide that is being used by your audience. If there isn't one, then pick the one you like—or make up your own style sheet from a combination of style guides. Just be consistent.