The best restaurants serving Fast food food in Brixton Hill Lambeth London

Loved Mc Ds strawberry milkshake, Bought one drank most but left about 1/4 when I went back into kitchen 2 hours later to throw out the liquid from milkshake but it was foam ? What the hell is in it

This place is surprisingly busy at 4 am but that is no excuse for the quality of service I received. Unfortunately my order was given to me incomplete and their indifference to me pointing this out w