Tel Aviv's march was not organised by an alliance of Islamists and leftists united around the ideas: stop the (Israeli) bombing; abolish Israel; victory to Hamas (the last two delivered euphemistically). The Tel Aviv and London slogans had a different political content (even as some of the words are the same).
In Britain we have an obligation to expose and make explicit the meanings and logic of the Gaza march organisers' slogans and politics. If that were to make us universally unpopular - so be it. We tell the truth.
But in fact our experience is different and more complex. We have become the target for abuse from some sections of the left and the Islamists - but the big majority of people (i.e. reasonable people who just attend) are fine with what we say. In some ways we're trying to give a fully-rounded political expression to the vaguely held views of very many on these demos.
So the SP, in an attempt to find the ear of the militant Islamic youth by toning down or avoiding appropriate and necessary criticisms of Hamas are failing to educate a much bigger group of people on these marches.