At first glance this looks like Jamie Wardley could be getting a ticket for drawing on the pavement, but that's not what is actually going on here. Jamie is being directed by his assistant in marking out the drawing. The large tripod (not a tripod as it has four legs) is being used to somehow correct the perspective during marking out, so that when viewed from the position of the tripod the drawing does not recede into the distance. The passing PCSO is taking a quick snap on his mobile phone to see if the theory actually works in practice.
Jamie is actually a sand and ice sculptor and made a huge sand sculpture of Charles Darwin in front of Bradford Town Hall a couple of years ago, I will try and post a picture of it in a day or two (I need to find the transparency and scan it).