To be fair a sniffer dogs job is not to be chasing. It picks out a scent. In general labs and springers are used as sniffers, GS to do the chasing if needs be.
Doesn't really matter if this in contravention of the Hunting Act or not, as it is rarely inforced. Even if the police were to decide they had broken the law, they are more likely yo give themselves a slap on the wrists!!!