Doing as the Romans do?

Might this happen in London? 'This' being a demonstration of more than 10,000 people to protest against the recent remarks of Iranian president Mahmoud Ahmadinejad, calling for the destruction of Israel. It took place in Rome yesterday, and was attended by politicians from both government and opposition parties, Jewish groups, the head of Italy's Muslim League, Iranian opposition activists and the mayor of Rome. There were also protests supporting Israel in Paris and Vienna. So it could happen in London too, since one can be critical of Israeli policy and still support its right to exist. (Would Ken Livingstone participate?)