Officer D2 is the second handler we see, who appears to have walked around the other side of the cycle racks to D1 to meet Tomlinson. He appears to have a radio or phone or some other dark coloured item attached to the left-hand lapel of his hi-viz jacket. He appears to be younger and leaner than D1, possibly in his twenties or early thirties, and appears to have some thin facial hair or thick stubble.
He too uses his dog (a black coated dog) aggressively towards Tomlinson, and can be clearly seen lunging at him, pulling the dog’s lead as he steps behind Tomlinson.
When Officer A strikes Tomlinson with his baton, D2 does not appear to be looking, but by the time of the shove his head seems tilted more in that direction.
By the time Tomlinson staggers off, D2 appears to be positioned to the front and left of the fountain.
[Edited to add links and more information, Thursday 23/4/9]