1)  You don't need to register with a lawfirm in order to be eligible
to receive compensation (if any) as a part of the class.  The various
lawfirms who are seeking a lead plantiff in order to gain standing.
Essentially they sue on one person's behalf, then broaden the suit to
cover the entire class.  Right now there are several lawfirms pursuing
this strategy with regards to Bodisen and to date no class (represented
by a lawfirm) has been recognized by any court of competant
jurisdiction.
2)  Compensation for shareholders in class action lawsuits is varied
and unpredictable.  In this case, since to date the lawsuits are only
against Bodisen with no third party defendants, there is a limit to the
value that can be distributed (no more than the value of what the
Company can pay).
3)  In the event that there is a settlement, there will be an effort to
contact class members.  The easiest way will be through your broker,
but the Court will also require that Bodisen advertise to find class
members.
4)  I am afraid that I have no sense of the listing requirements of the
London stock exchange.  Typically, these listing requirements include
minimum market capitalization, and reporting requirements (similar to
the AMEX) but I do not know the London stock exchange requirements and
do not know the status of any action (if any) that the London stock
exchange has taken with regards to any delisting procedures.

I hope this helps.