GM's local unit Vauxhall will modify the park brakes on about 250,000 cars after the consumer advocate reported problems with runaway vehicles last year, UK group Which? (similar to Consumer Reports in the US) said ahead of the publication of its latest magazine this week.

Owners of manual-transmission Vectras and Signums produced since 2002 are being told to contact their nearest dealer for a free modification, Which? said in a statement. Vauxhall confirmed the modification programme was under way.

Which? said that, after it first reported on "more than a dozen" incidents of parked vehicles rolling away last July, and had "dozens of other complaints", Vauxhall maintained it could find no fault.

At the time, GM UK spokesman Denis Chick told just-auto that the company would write to owners reiterating handbrake application instructions already contained in the owners manual. He also noted that another manufacturer had recently done the same thing, though no faults had been found with its vehicles, either.

"But it's now found that if you apply the handbrake by depressing the release button, the mechanism could be left partially released," Which? said in a statement ahead of the publication of its latest magazine this week.

"The company still maintains its handbrakes are safe, but says it will modify mechanisms to 'reduce the possibility of a partial release when incorrectly setting the handbrake'. "

Chick said in a statement sent to just-auto on Friday said that, "following a small number of complaints of Vectra and Signum vehicles rolling away due to allegedly ineffective handbrakes, Vauxhall Motors Limited engineers, along with consultant engineers, suppliers and other bodies, have conducted rigorous technical tests on those vehicles.

"During its extensive test programme, Vauxhall reviewed a number of handbrake mechanisms and found that when the handbrake is applied by depressing the release button, it is possible to manipulate the handbrake mechanism so as to cause it to release partially.

"Vauxhall advised customers in October 2007 that when parking their vehicle, customers should always apply the handbrake and engage a gear in line with the recommendations referenced in the owner's manual and in the official Highway Code, especially when parking on a slope.

"Vauxhall believes that the handbrake system used in the Vectra and Signum is safe, however, Vauxhall treats all matters relating to the safety of its products as its highest priority.  In line with this priority and that of continuous improvement, Vauxhall has decided to implement, as a customer satisfaction programme, a modification to the handbrake mechanism to reduce the possibility of a partial release when incorrectly setting the handbrake.

Owners of circa-250,000 manual transmission Vectra and Signum models (produced from 2002) will receive a letter from the company requesting that they contact their nearest retailer to arrange for the modification, at no cost to the customer.

"Vauxhall Motors Limited is launching this customer satisfaction programme in agreement with the Vehicle and Operator Services Agency.  Note that this is not a safety recall."

Vauxhall stressed that, irrespective of the modification, when parking their vehicle on a slope, customers should continue to engage a gear when the vehicle is stationary and apply the park brake without depressing the release button.

Vauxhall denies park brakes faulty