That's not exactly what Sadiq Kahn said. He made a comment when visiting New York when asked about how New York was having to up security measures due to the terrorist threat. He replied that the danger of terrorist attacks were now part and parcel of living in a big city and that cities needed to address that. It has been taken out of context ever since and used against him.
If someone changed their name to Allahu Akbar... their mate could technically get shot for shouting them in Venice..
Khan was actually saying this in September of last year, the irony is of course that there have been a number of terrorist incidents since then with sadly loss of life, the reality is that we have been living with the treat of terrorism for the last 50 years or more, the IRA and other groups in the UK, Basque terrorists in Spain, Baader Meinhoff and so on up to the Islamic terrorists.
This makes me think about when the London attacks were happening, and there was the rumour that there was another terrorist incident ongoing at another location in the city. Then a couple of hours later we were told to relax, it was just a normal London stabbing and nothing to worry about. Crazy way we look at things in the modern era.
To be honest somewhat both right. Before ISIS we had IRA so, yes, if you live in a big city you're more likely to feel the effects of terrorism. And yes shouting Allahu Akbar will get you shot pretty much anywhere at the moment. Neither needed to be said by supposed politicians though
For many non-religious people like me, the term Allahu Akbar is fast becoming synonymous with a war cry before some nutter commits murderous acts on behalf of their religious beliefs. If circumstances dictate that Police shoot first and ask questions later, so be it.