The fatal crash of a double-decker coach near Heathrow Airport has thrown the spotlight on the safety record of the type of bus involved - the Neoplan Skyliner.
Twelve double-decker coaches withdrawn from service following the crash have passed safety checks, but will not be put back in use until further investigations from National Express are completed.
There are differences between the continental and British coaches
The Skyliner is described as a "pioneer" that can "confidently set the standard for double-decker coaches" on the website of its German manufacturer, Neoplan.
"When you board the Neoplan Skyliner it feels like being in an aeroplane," the site says.
"The elegant interior design could easily be in the first class of a passenger jet."
The site also describes coaches - which are more than 12m (39ft) long and 4m high - as having "comprehensive" safety features.
Following the Heathrow crash, Neoplan offered condolences to everyone involved and said they would "assist in every way" to work out what happened.
In a statement, the company defended the safety record of the Skyliner and said they knew of "no technical reasons for the crash at this time".
The firm said: "The Neoplan Skyliner has an excellent safety record and is in successful service by many leading operators, not only in the UK but across Europe.
"We believe there should be no concerns among passengers regarding their safety due to the technical performance of these vehicles."
Twelve double-decker coaches were withdrawn from service after a National Express coach crashed on the M25.
But all have now passed safety checks, according to manufacturers Neoman.
The company said the coaches were thoroughly examined and said there should be no concerns among passengers regarding their safety.
The bus group said in a statement: "Neoplan double-deck-vehicles operating in the National Express fleet have been examined thoroughly overnight.
"As expected, all have passed these safety checks and are available for immediate return to service as and when the operator wishes."
But National Express said the fleet will not be returned to service until it had completed its own investigations.
The Skyliner was developed as a luxury tour coach in the 1960s
Stagecoach - one of the UK's largest bus firms - operates 50 Skyliners on its Oxford Tube and Megabus routes.
A spokesman stressed that they have had no problems with the vehicles since introducing them in 2004, and that Stagecoach's Skyliners are not identical to those used by National Express.
He said: "All of our vehicles are subject to a rigorous 14-day in-house maintenance regime, which is more stringent than the legal regulations.
"We take the safety of our people and our passengers very seriously."
There are between 30 and 40 further Skyliners on Britain's roads run by smaller travel firms.
Safety concerns about double-deck coaches had been raised as long ago as May 2003, when a similar vehicle crashed in southern France and 28 people died.
Newspaper reports have claimed that Neoplan now fits left-hand drive Skyliners with a safety system called electronic safety control, whereby each wheel brakes separately.
The Times claimed that this system was not in place on the type of coach that crashed this week.
Neoplan said there are "design differences" between the left-hand drive and right-hand versions of the Skyliner, but they were unable to confirm specifics.