General Motors Europe’s UK unit Vauxhall has insisted the launch of the Ampera, its version of the Chevrolet Volt, is on track and order books will open soon with first deliveries scheduled to start in May 2012.

A spokeswoman said an earlier reported postponement of an increase in production planned for this month at the Detroit Hamtramck plant that makes the Volt and Ampera would have no effect on the UK launch timetable. The factory was scheduled to double output to 3,200 cars a week to meet the expected rise in demand from Opel and Vauxhall Ampera sales starting in Europe.

The reported delay came in the wake of battery fires following crash tests in the US. GM and US safety regulators are trying to determine why two of the car’s lithium-ion batteries caught fire a week or more after being crash-tested by the National Highway Traffic Safety Administration (NHTSA). GM said the batteries can be made safe by draining the power after a severe crash.

The Ampera has already been awarded a top five-star rating in the latest round of Euro NCAP test results, announced last week.