I am horrified and frightened by Cameron's actions. He has not managed to protect the City and had almost certainly severely damaged it.
The treaty that Cameron vetoed would not have affected the City. The issue of the Tobin tax was not part of the Treaty, and can still go ahead. he has NOT stopped it nor any of the other regulations.
The Treaty was to rescue the Eurozone. He tried to hold the Eurozone to ransom unless they made some changes to existing regulations. He stated that he would not allow the others to put in place measures to rescue the Eurozone unless they changed existing policy on financial regulation. That is, he tried to take advantage of the EU crisis for his own ends. This is despicable - akin to refusing to take an injured man to hospital until he gives you his wallet. With that attitude I am not surprised that they told him to go away. The French and Germans are right to take the moral high ground.
Britain's ability to stop any of the financial regulations is now much weaker than before. In order to stop them, we need to get other countries onside. Given Cameron's actions, who would want to help him? In any case, Cameron will not be there when others are negotiating. If you are not at the table, you cannot influence it.
The logic of Cameron's actions is to leave the EU altogether. This would be an economic disaster for the City. Many foreign banks are in the City as this is a good way to access the world's largest market - the EU. With Britain on its own, this attraction will go. Plus don't forget the business service sector, which largely exists to service the EU. And manufacturing etc... We will be Iceland without the fish.
The worst thing is, that exiting the EU may no longer be Britain's decision. He is forcing the others to set up new institutions which Britain will not be part of. There may be no way back.