I don't think they're lying but you have to look really hard on their quite comprehensive website to find any mention of the beth din and no mention of christianity's influence over the supposedly secular law in the UK (laws on gay marriage, prostitution, even drugs, could be argued to have a basis in protestentism - although im not seriously suggesting they should muddy the waters to that extent)
a strong multi-faith (or ex-faith) march calling equally for no sharia, end the beth din and the disestablishment of the CofE would have put clear blue water between them and the EDL, would seem less provocative to moderate muslims or those using sharia appeals as a tool of relative empowerment (as jeff points out early in the thread) and would place the debate about sharia in the UK in context
now its possible something like that could come out of this, but i suspect not, and i further suspect this is more about promoting the agenda of the IWCP on the back of recent headlines