Environmentalists now fear that the UK government's draft energy bill to be published on Tuesday will end in a new "dash for gas".
They want the bill to be guided by the government's stated wish to almost completely de-carbonise the electricity industry by the 2030s.
But there has been no guarantee such a target will be enshrined in the bill.
The environmentalists say ministers' problems with new nuclear power will leave the UK gas-dependent for decades.
The UK could buy emissions permits on the European market to keep to its medium-term emissions reductions targets.
But a failure to de-carbonise electricity would divert the Britain from its course to cut CO2 by 80% by 2050 - unless the gas-fired power stations were made to run with carbon capture and storage, a technology that is unproven on a large scale.