Place where Harvey and Kate agree to meet again?

As the synopsis goes, following the wedding reception, Harvey and Kate walk and talk until dawn ending up in what appears to be a lovely, colourful square. They sit on a bench before kissing and agreeing to meet exactly in the same place at noon. I have been trying to locate the place in London. I've visited the city plenty of times yet I've never seen it. Anybody know what its name is?