The proposed method of operating train doors on Southern Railway, which is at the centre of a long-running industrial dispute, is "a safe method of working", according to the rail regulator.
Transferring the responsibility for opening and closing doors from train conductors to drivers would meet the legal requirements for safe operation as long as suitable equipment, procedures and staff are in place, the Office of Rail and Road (ORR) said.
Transport Secretary Chris Grayling described it as "a powerful report" while Southern's parent company, GTR, said it welcomed the findings.
But the Rail, Maritime and Transport (RMT) union, which has called a number of strikes over the issue in recent months, claimed it was a "complete whitewash" and accused the ORR of being "nothing more than an arm of Government".
An ORR official carried out inspections on the Horsham to Bognor Regis route in West Sussex, where Driver Only Operation (DOO) of train doors has recently begun.
It was found that although the quality of in-cab CCTV images of platforms varied, all were "adequate".
A recommendation has been made to Southern to make improvements so that image quality is "consistently high", including overhauling the cleaning regime of external camera lenses.
Ian Prosser, HM Chief Inspector of Railways, said: "Following a thorough review of GTR-Southern's method and implementation of Driver Only Operation, ORR is satisfied that with suitable equipment, proper procedures and competent staff in place, it is a safe method of working."
Mr Grayling said: "This is a powerful report from the independent rail regulator that confirms that Southern's plans for driver-controlled trains are safe.
"We should never stop trying to make our railways safer, and that is why the ORR has followed their review with recommendations on how GTR can go even further to improve the safety of train dispatch.
"The operator has accepted these in full and I have made it clear to them that I want these implemented as soon as possible."
On Wednesday the Aslef union announced that strikes by Southern Railway train drivers will hit the network at the end of January, as well as next week, causing fresh misery for hundreds of thousands of passengers.
Mr Grayling said he has written to the unions again to ask them to suspend "this needless strike" and claimed the ORR's report should encourage both sides in the dispute to "get back round the table for talks".
Charles Horton, chief executive of GTR, said the ORR had produced a "robust report" which included "a thorough risk assessment".
In light of the ORR's findings the unions must acknowledge that they have "no credible argument" that DOO is unsafe, Mr Horton claimed.
But RMT general secretary Mick Cash said: "The report into Driver Only Operation on Southern Rail issued by the ORR this morning is a complete whitewash that proves conclusively that the Office of Road and Rail is no longer fit for purpose and is nothing more than an arm of Government, wholly committed to propping up the train companies and the Department for Transport.
"The authors of this report have taken no evidence from the trade unions, have swallowed whole the distorted pictures painted by Southern Rail and have limited their work to the issue of door control when there is a whole raft of safety issues that are allied to the question of Driver Only Operation.
"That is scandalous."