The regulator, NHS Improvement, said it wanted more progress after the NHS had slipped behind schedule in its efforts to reduce the agency bill.
Last year £3.6bn was spent on agency staff, but the regulator wants that brought down by £1bn by the end of this financial year.
A cap was introduced in October and has so far saved £600m, the regulator said.
It means hospitals, mental health trusts and ambulance services should not be paying more than 55% above normal shift rates for any staff, from doctors and nurses to administration staff. Only senior managers are exempted.
The aim was to reduce the overall cost of agency staff as well as getting hospitals to reduce their reliance on them.
Agency staff are more expensive because the NHS has to cover the agency fees and employers costs, such as National Insurance contributions, when it buys them in.
NHS Improvement said the progress being made was "promising", but it still leaves the NHS short.
The latest accounts suggested NHS trusts were 10% down on where they wanted to be.
And while the agency bill is falling it is not yet clear whether spending on other parts of the pay bill has risen.
The figures released by NHS Improvement do not cover NHS "bank" staff - effectively the health service's in-house agency - or money spent getting employed staff to do overtime.
NHS Improvement said it would start publishing "league tables" of the best and worst-performing trusts on agency spending later this year.
Information on the 20 highest-earning agency staff per trust would also be collected amid suspicion some people are still earning large sums from agency work.
It found examples of hospitals being quoted double the rates for doctors. In one case a trust was quoted £130 an hour for a surgeon when the cap is meant to be £76, while another was quoted £70 an hour for a junior doctor when the fee is meant to be £35.
NHS Improvement chief executive Jim Mackey said: "The NHS simply doesn't have the money to keep forking out for hugely expensive agency staff. There's much more to be done."
NHS bosses are threatening to "name and shame" trusts in England as they try to crack down on agency spending.