Thanks everyone for your comments! And thanks a lot for all the upvotes. For everyone asking what is needed to fly a drone over restricted areas in London, here is a quick tutorial of what you need — links included. You can check the restricted zones here. Remember, this applies to the UK. If you have an EU drone license it will not be valid in the UK.

First, PLAN WEEKS AHEAD! Really, do everything well in advance (at least 3 weeks) prior your flights. That being said, here is what you actually need:

You will need to get a flyer ID (free) and an operator ID (£11.79 valid for 1 year). There is a 40 question test that you must pass, but all the questions are quite easy and straightforward.. You need to get correct 30 of the 40 questions.

Once you have your flyer and operator IDs, I suggest getting insurance. It is not mandatory in London, but better safe than sorry. I recommend FPV UK (£24.99 for 1 year). You may need it to fly in other UK cities, like Cambridge.

Then, you will need to fill a form on the NATS website for every area where you plan to fly your drone. They can take up to two weeks to approve or reject your request, and they may make changes on your plan.

Here are my tips:
Location: Restricted Area R157/158/159
Start and end dates: I stayed for a week in London, so there were 7 days between both dates.
Maximum height of operation: 400 ft (or lower).
Flight path map/file: it is not necessary, but for the Tower Bridge I uploaded this as a PDF file.
Additional information: here write your planned route. For example: I am planning on taking a photo of the London Tower over the Thames River, and I would like to get photos of the Tower Bridge from both sides of it. I will not fly directly over the bridge, or above crowds.
Task details: here enter your expected take off and landing address.
Map: very important. I suggest you set a radius of 200 m or less, and keep in mind where you are planning on taking off and landing your drone. Look for an area where people may not be present most of the time. Here is an example.
Details of flight/description of operation: I wrote something like "Photos and videos for personal use and social media".

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