A group of masked protesters have become "aggressive" towards police at Canary Wharf shopping centre.
Police have issued an order to "prevent people concealing their identity with masks" and have made several arrests.
They said: "We have made three arrests for common assault, possession of drugs and assault on police/public order offences.
"One of our officers was punched in the face - luckily they have not suffered significant injury."
Video seen on social media showed young children among the protesters, with some of them wearing England flags.
Officers said: "We are aware there are young children in the protest area and while we deal with any criminality our officers are ensuring the safety of them is paramount."
Police have also sent extra officers to deal with the demonstrations