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."

The Colombia international, who has not played since October following a thigh injury, has been replaced in the squad by new loan signing Alexandre Pato.
The 29-year old has made just one Premier League start since signing on a season-long from Monaco last July.
Former AC Milan forward Pato, 26, signed for Chelsea last week on a six-month loan from Corinthians.
However, the Brazil international has not featured since November as he looks to regain full fitness following a series of injuries.
Chelsea interim boss Guus Hiddink has also included new signing Matt Miazga in both his Champions League and Premier League squad lists for the second half of the season.
The United States defender, 20, joined Chelsea on a four-and-a-half-year contract from New York Red Bulls last week.
Falcao, who was linked with a deadline day move to former club Atletico Madrid, has been named in Chelsea's 25-man Premier League squad.
Manchester City manager Manuel Pellegrini revealed on Monday that Nigerian forward Kelechi Iheanacho, 19, will replace Samir Nasri in City's 25-man Champions League squad.
France international midfielder Nasri, 28, is set for at least another two months on the sidelines following a hamstring injury and tendon surgery in November.
Clubs featuring in the knock-out stages of the Champions League were required to supply European football's governing body Uefa with their updated squad lists by Tuesday night, but Arsenal have yet to publicly announce any changes to their 25-man squad.
The Gunners are expected to make one change, with new midfield signing Mohamed Elneny, 23, replacing defender Mathieu Debuchy, 30, who has joined Ligue 1 side Bordeaux on loan until the end of the season.
NHS bosses are threatening to "name and shame" trusts in England as they try to crack down on agency spending.
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Radamel Falcao has been omitted from Chelsea's 25-man squad for the Champions League knock-out stages.