The European Commission yesterday imposed a $37 million (€43.45 million) fine on Opel Nederland, a subsidiary of US car company General Motors, for preventing customers from abroad buying cars in the Netherlands.

Mr Mario Monti, the European Union's competition commissioner, said the case was a "very serious infringement of European competition rules and must be dealt with severely".

The Opel fine is not as big as the record €102 million fine imposed on Volkswagen in January 1998 for prohibiting non-Italian customers buying cars at its dealers in Italy. But the Commission said this did not indicate a more lenient approach. It also took into consideration the length of time the company had infringed the single market rules and its co-operation during the investigation.

The EU regulator said Opel had obstructed exports of new cars to consumers from outside the Netherlands between September 1996 and January 1998.

The investigation followed dawn raids on Opel's Dutch headquarters and two dealers in the Netherlands in December 1996. The Commission has had hundreds of complaints from consumers about their inability to buy cheaper cars abroad - notably from potential German and UK buyers.

"The Commission is determined to intervene in cases where measures taken jeopardise the proper functioning of the single market," said Mr Monti, stressing that the right to buy products more cheaply in another member country was one of the main benefits of the single market.

Consumer organisations have alleged that car companies are running an elaborate cartel to maintain high prices in countries such as the UK.

A Commission spokesman said there was another formal investigation under way into Daimler-Chrysler's sales strategy in several EU countries, but it was unlikely to be concluded this year.

He also said officials were examining material gathered in dawn raids on Peugeot and Renault, indicating similar sales practices. The Court of Justice upheld the Commission's case against Volkswagen, but on appeal reduced the fine to €90 million.

Nissan warned yesterday that the strength of sterling and the cost base at its UK plant near Sunderland meant it might not be competitive to assemble the new Micra in Britain.

Officials said that both Nissan's existing Barcelona plant in Spain and Renault's plant in Flins, France, were better placed to build the Micra at a profit.