I believe in UFO's. But this one is either edited or a government plane or craft. That's experimental or just showing off to the public.
Reasons why I don't believe this is an Aliens Spacecraft
1. Aliens will probably not showboat and act flashy flying around in random areas, especially in a world that their not familiar with.
2. If ever aliens reach our planet, it only means one thing. THEIR TECHNOLOGY IS VERY VERY VERY ADVANCED!
Meaning they're not stupid! And just show themselves to us without a plan.
3. If this is real. EVERYONE in the world is probably talking about this right now. And every government in the world is pretty much doing some drastic security measures and the media is probably going crazy right now in TV, Radio and The Newspaper.
4. If an alien spacecraft flew in that area. In this case it's London,one of the richest countries in the world.
Meaning MOSTLY EVERYONE in that place has some sort of Camera. Almost every phone right now has one.
Logic in this is. There will probably be more than a dozen if not hundreds of video shots done by different people and uploaded to the internet right now, since the flying object flew for more than a minute giving enough time for people to whiff out their cameras and take a picture or video of it. Instead we have only one.
Isn't he a lucky bastard.
The chance of this is, it would probably be alot easier to win lotto 3 times in your lifetime than that to happen.
5. I could go on and on for simple reasons why this is not an alien saucer.
LIKE I SAID I ALSO BELIEVE IN "THERE ARE OTHER BEINGS AND LIFEFORMS OUT THERE" just not this video.