argh!!
i'm at a loss for words trying to write something...
basically it goes like this:
oi... this working group is changing their focus, not our
division's business anymore.. you want to take over representing
our department in this working group or not? if not, we tell them
our department is pulling out of the working group... if you want
to continue, you go yourself...
but how to make it sound formal and businesslike?
Actually your version is clear enough what. 
Dear tan ah gao,
This working group has changed their focus to (whatever it
is) , which is no longer in line with our division's core
business.Would you like to take over as our department's
representative? If you do not wish to, or are unable do so, we
will be pulling out of the working group.
Best Regards,
ah Bear
