Mr Trickett described the deal with CW as “an interim arrangement that can allow the savings to be delivered”.
However, he said there would be no merger with that board at this stage because the government wanted health boards to align with strategic mayoral authorities.
Some savings would be made by not having to service NHS England’s infrastructure, Mr Trickett added.
He said the role of the board was also changing, with staff being asked to be less “hands-on” as it becomes a more strategic commissioner.
“The NHS in this part of the country is far from perfect, but we have made some good progress,” Mr Trickett said. “We want to continue that.
“I won’t be willing to compromise things that make a difference for patients, to hit this target.”