Nine out of 10 Volkswagen drivers in Britain affected by the diesel emissions scandal believe they should receive compensation, increasing the pressure on the carmaker as it attempts to recover from the crisis.

Almost 1.2m diesel vehicles in Britain are involved in the scandal, out of 11m worldwide, and VW faces a hefty bill if it is forced to make payouts to motorists. The company has put aside €6.5bn (£4.8bn) to deal with the cost of recalling and repairing the affected vehicles, but it also faces the threat of fines and legal action from customers and shareholders.

There is a growing frustration among VW drivers in the UK over the lack of information about how their vehicle will be repaired, according to the consumer watchdog Which?. VW has sent letters to affected customers, arriving this week. However, the letters state that the company is still working on its plans and another letter will be sent when these are confirmed.

Paul Willis, the managing director of VW UK, told MPs on Monday that the recall of vehicles may not be completed by the end of 2016 and that it was premature to discuss compensation.

However a survey by Which? has found that nine out of 10 affected motorists want compensation.

Richard Lloyd, the executive director of Which?, said: “Many VW owners tell us they decided to buy their car based on its efficiency and low environmental impact, so it’s outrageous that VW aren’t being clear with their customers about how and when they will be compensated.

“Volkswagen UK must set out an urgent timetable for redress to the owners of the affected vehicles. We also need assurances from the government that it is putting in place changes to prevent anything like this happening again.”

In the wake of the scandal, 86% of VW drivers are concerned about the environmental impact of their car, while 83% questioned the impact on its resale value and 73% feared the performance of their vehicle would be affected. More than half of the VW customers said they had been put off from buying a VW diesel car in the future.

A total of 96% stated that fuel efficiency was an important factor in buying the diesel vehicle, while 90% said it was the seemingly limited environmental impact. Both these issues are affected by the scandal. Which? surveyed more than 2,000 motorists who bought a VW diesel car between 2008 and 2015.

In further developments, VW has admitted that US regulators are examining an additional piece of suspect software in its 2016 diesel vehicles. The “auxiliary emissions control device” heats up a pollution control catalyst faster, boosting the performance of the device that separates nitrogen oxide into harmless nitrogen and oxygen gases.

A VW spokesman confirmed that the company reported the device last week to the Environmental Protection Agency, which discovered the initial defeat device that allowed the company to cheat emissions tests.

The regulator is now considering whether to approve the device or if it is another defeat device, designed specifically to manipulate the performance of the vehicle during tests. VW’s new 2016 models cannot be sold until they are approved by regulators and thousands of vehicles remain marooned in ports as a result.

In a separate setback, the company also confirmed that the executive earmarked to become boss of VW in North America has left the company. Winfried Vahland, the head of the VW-owned Skoda brand, was due to become head of a newly formed North America arm, bringing together its businesses in the US, Canada and Mexico.

Vahland would have led the company’s fightback in the US alongside Michael Horn, the head of VW in the US. However, the company said Vahland was leaving due to “differing views on the organisation of the new group region”. VW insisted his departure was not linked to the emissions crisis.