Sadly, I fear that those involved may have been influenced by the attitude and behavior of US personnel. If there is anything positive to come out of this it is surely a requirement for other governments in the coalition to make it a condition of their active participation that standards of treatment of those in custody are acceptable to all parties.
There are other issues of concern about American behavior (friendly fire, direct shooting of journalists, and use of excessive firepower causing unacceptable collateral damage to name a few) but this one is pervasive. Lets us be frank (for the sake of the many victims in awful situations) – the Americans have a long history of downright barbaric treatment of detainees – from the Rhine camps (at the end of WW2) to the containers in Afghanistan (remember them?) – episodes that make Guantanamo Bay seem like Butlins.
If UK personnel are to support them in future, working closely with them, then the US must lift its game.