The European Commission said subsidies paid to Drax may have violated rules on state aid

Plans to convert Britain’s biggest power station to run on greener fuels were in jeopardy last night after the European Commission ordered an “in-depth investigation” into a possible violation of state aid rules.

The giant Drax plant in North Yorkshire, which was built in the 1970s and runs mainly on coal, has already converted two of its six units to burn wood pellets as part of a drive to generate more of its electricity from greener fuels.

It wants to convert at least another unit to burn wood, a fuel that also allows Drax to qualify for generous subsidies under the terms of a 2014 agreement with the government to help to fund the project.

In a statement, the commission expressed concern that the subsidies