The incidents of alleged petrol stretching has dropped in the last two months, according to new figures.

But despite 134 allegations in the past seven months, illegal stretching agents were found in just two samples which were both from the same outlet.

Reported incidents of stretching, where kerosene is illegally added to petrol and then sold at fuel stations as standard petrol, peaked in November at 42.

Reported cases dropped to 11 in December and six this month, with a total of 134 allegations of petrol stretching in the last seven months, according to figures released by Minister for Finance Michael Noonan.

He said the Revenue Commissioners had, since last summer, “received reports from a variety of locations around the country of problems relating to petrol quality and suggestions that these problems are attributable to petrol stretching”.

However, “despite extensive testing by the State laboratory, evidence of a prohibited stretching agent has been found in only two samples, both taken from one site”, he said. The results in this case were conclusive and “a file is being prepared with a view to prosecution”.

Mr Noonan told Independent TD for Roscommon-South Leitrim Denis Naughten that further tests by the State laboratory showed traces of road diesel in several samples from various locations.

In a written reply to a parliamentary question, the Minister said there was “no rational economic reason or fraudulent incentive” for anyone to mix normal road diesel with petrol. He added that this diesel contamination “could have taken place well ahead of the problems related to fuel quality that manifested themselves in vehicles”.

The Minister also said the Revenue Commissioners, on an ongoing basis, undertake “an extensive programme of compliance and enforcement actions to ensure adherence to the legal requirements governing the supply and sale of mineral oil”.

He said this includes visits to mineral oil traders when they examine transport and movement documentation and take samples of fuel for analysis.

Up to last October Revenue received 31 complaints about petrol stations in the west; in counties Mayo (15), Roscommon (eight) and Galway (four).

TDs in western counties, the border area and the midlands have repeatedly raised the issue in the Dáil about the number of complaints they receive about alleged stretching, where the engines of new cars in particular, had been destroyed by kerosene being added to the fuel.