Hundreds of thousands of people have marched through central London, calling for a second Brexit referendum. After three years of negotiations, it is still unclear how or when the United Kingdom should leave the European Union. For many protesters in the capital, it is the biggest political crisis in a generation as Prime Minister Theresa May struggles to unite parliament behind her Brexit plan. Al Jazeera's Sonia Gallego reports from London. Subscribe to our channel: http://aje.io/AJSubscribe Follow us on Twitter: / ajenglish Find us on Facebook: / aljazeera Check our website: https://www.aljazeera.com/ #Brexit #BrexitMarch #PutItToThePeople