Instead, the European Aviation Safety Agency (EASA) will run its own tests on the plane before approving a return to commercial flights.

The 737 Max has been grounded since March after two fatal crashes and investigators were a little alarmed to discover the cosy nature of Boeing's relationship to US regulators.

The regulator had been passing off routine tasks to manufacturers for years, with the goal of freeing up specialists to focus on the most important safety concerns. But on the Max, the regulator handed nearly complete control to Boeing.

But Easa told the US Federal Aviation Administration (FAA) there would be "no delegation" on safety approval in a letter sent on 1 April. Patrick Ky, Easa's chief executive, revealed a list of four conditions given to the US authorities in a presentation to the European Parliament's committee on transport and tourism on Monday.

Europe's tough stance is a blow to Boeing's hopes of a rapid return to service for the 737 Max, and is also a significant break with the established international practice of aviation regulators accepting each other's standards.

A spokesperson for the FAA said it had "a transparent and collaborative relationship with other civil aviation authorities as we continue our review of changes to software on the Boeing 737 Max."

"Our first priority is safety, and we have set no timeframe for when the work will be completed. Each government will make its own decision to return the aircraft to service, based on a thorough safety assessment."