The Civil Aviation Authority (CAA) said safety is its "number one priority" after a poll by the pilots' union Balpa showed more than a half had fallen asleep while in flight.
A CAA spokesman said: "We think the new European flight-time limitation regulations maintain the UK's current high safety levels, and will actually increase safety for UK passengers travelling on some other European airlines.
"The changes will give the CAA far greater access to airline data to help us oversee fatigue risk management. We will shortly begin working with UK airlines over the introduction of the new system."
UK pilots' organisation Balpa said last month's incident "comes as no surprise", adding that it had "repeatedly warned the CAA of the risk of both pilots falling asleep, including in a letter to each member of the CAA board last year".
Balpa general secretary Jim McAuslan said: "British pilots want to make every flight a safe flight and tiredness is the biggest challenge they face.
"As the regulator responsible for UK flight safety, the CAA has been far too complacent about the levels of tiredness among British pilots and failing to acknowledge the scale of the under-reported problem.
"In fact, the CAA and Government are backing EU cuts to UK flight safety that will increase tiredness among pilots and the risk of dangerous incidents."
The CAA said today: "We understand that Balpa are not happy with the proposals but we think overall it is a good package and not much different to what we have now."
Both pilots on an Airbus passenger plane were asleep at the same time with the UK-operated aircraft flying on autopilot.
One of the pilots indicated in a report to the UK's Civil Aviation Authority (CAA) that the pair nodded off after both had only five hours sleep in the previous two nights.
Details of last month's incident, on August 13, come at a time when UK pilots' organisation Balpa is unhappy at proposed European changes to flight-time regulations.
This was a serious incident but an isolated one. I think lessons will be learnt from this. We are circulating this report within the industry.
We don't know why the pilots had had so little sleep before this flight. They were taking it in turn to have rest periods, with the one always checking the autopilot and it looks as if both fell asleep at the same time.
– CAA spokesman
Details of the incident, logged by the CAA as a mandatory occurrence report, were obtained by a news agency which had asked for incidents of pilot fatigue.
The CAA did not say which airline was involved nor where the aircraft, an Airbus A330, was travelling.