Yep, it is used in English. Refer to the mobbing encyclopeadia at http://www.leymann.se/ or http://www.mobbing-usa.com/

Definition: EMOTIONAL ABUSE at the workplace.

"Ganging up" by co-workers, subordinates or superiors to force someone out of the workplace through rumor, innuendo, intimidation, humiliation, discrediting, and isolation.

Malicious, nonsexual, nonracial harassment.

It also means to crowd around and jostle, annoy, etc, as in curiosity or anger.

Webster's New World Dictionary

.. in great numbers either to attack or to admire!

In modern British English, it is only commonly used in the 2 situations:

1. to crowd around in admiration (e.g. around a film star)

2. (of animals, especially birds) to harrass, in a group, a predator on the group or an animal competing with the group for food.

NODE – The New Oxford Dictionary of English gives more or less the same two definitions John mentioned from Collins but the current NODE is now over four years old.

Webster's Online Collegiate, which is normally quite up-to-date, shows only roughly the same definitions as NODE and Collins:

"Main Entry: mob
Function: transitive verb
Inflected Form(s): mobbed; mobbing
Date: 1709
1 : to crowd about and attack or annoy <mobbed by autograph hunters> <a crow mobbed by songbirds>
2 : to crowd into or around <customers mob the stores on sale days>"

Over 400 hit Google, English, domain .uk, hits for "mobbing" though lead me to think that the term is in worldwide use, that is, also in the UK.

http://www.google.de/search?as_q=mobbing&num=100&btnG=Google...

The same search with "-bird" and "-animal" still draws over 200 .uk and over 3000 .com hits.

A similar, often used, and easily understandable term is "adult bullying". The problem is only that "adult bullying" might involve a mob or just one person.

According to this site, the "bully" is usually singular:

http://www.successunlimited.co.uk/books/biscouns.htm

and therefore "bullying on the job" may not always be synonymous with "mobbing".

The Google results and Andy's Swedish/American site references indicate however that you can use "mobbing" worldwide with the meaning of:

"Mobbing can be compared to bullying at the workplace. Mobbing denotes, however, more specifically a "ganging up" by co-workers, subordinates or superiors (all plural!) to force someone out of the workplace through rumor, innuendo, intimidation, discrediting, isolation, and particularly, humiliation. Mobbing is a serious form of nonsexual, nonracial harassment (by a group!). It has been legally described as a status-blind harassment (by a group!)."

The bits in parentheses and italics are from me.

A search for "mobbing" together with "workplace" yields over 1000 hits from everywhere. Many about Leymann.

It appears that "mobbing" is an old English term for the group attack procedure of animals and birds that achieved worldwide use in many languages. The term has now been resurrected for use in workplace surroundings. Because of the worldwide familiarity with the original animal use, the workplace use seems to be taking place everywhere at more or less the same time. The beginning of this new/old/new use of "mobbing" in workplace situations was apparently not in the UK or US but Sweden:
http://www.psypress.com/BKFILES/0863779468.htm

"In recent years, mobbing (bullying or harassment),a severe form of social stresses at work, has become a topic of tremendous public interest in several European countries. Mobbing includes minor social conflicts such as socially isolating a person, rumors, or giving somebody a bad name, but also massive conflicts like giving someone no work or work below or above one's qualification, threats to kick somebody out of the firm or threats of physical violence. Although mobbing is a very old phenomenon, it has not been described and systematically investigated until the early 1980s when Heinz Leymann started the first research projects in Sweden."

The most informative site I could find was, as a matter of fact British, but based on German and Swedish sources:

http://www.law-office.demon.co.uk/mobbing1.htm

HTH

Dan