I would 100% say a Mottled Orpington. I'm holding off on the English part because it's not showing much in the way of floof.
How old did they say this bird is? Did it recently molt? I ask because the tail is still coming in. There's also down showing in the saddle area.
How old did they say this bird is? Did it recently molt? I ask because the tail is still coming in. There's also down showing in the saddle area.