The fall of London

Since the Brexit referendum in 2013, people have been talking about how London will lose its significant position in the financial world. This year, London has slipped even further behind New York; however, we also need to notice that before New York took over London as the world top financial centre according to the global financial centres index compiled by consultancy Z/Yen, London was the world financial capital for five straight years despite the Brexit referendum in 2013. Why did London start falling recently rather than earlier?
First, many “leave" campaign politicians promised a bright future for Britain leaving the European Union. These promises could maintain some degree of market confidence and mitigate the shock brought by the referendum result. Secondly, shortly after people learning the referendum result, people expected a talk and a deal between the UK and the EU and the prime minister at the time, Theresa May, promised the British population a satisfactory deal between the EU and the UK. Right now, it seems that the probability of a no-deal Brexit is increasing as approaching the 31st of October, since both the split between the UK and the EU and the split within the Parliament seem widening even after a new prime minister took the office. Thirdly, it seems we are approaching the date of Britain leaving the EU for real this time. Companies including financial firms and institutions are more anxious to make a response to the changing outside environment than previously.
Overall, if there is a fall of London, the troubling handling of the Brexit could be the most significant factor in this, since London remained as the world financial capital after the Brexit referendum.