Coal-fired power accounts for a third of UK electricity generation, the highest it has been since 1996, Lord Chris Smith told the BBC.
He warned that unless this trend was quickly turned around, the UK would miss its climate change targets.
Smith said that the move towards gas in the US had seen the now-cheaper fuel gobbled up by European power generators.
UK MPs will vote on a motion next week to remove almost all carbon pollution from electricity generation by 2030.
Lord Smith urged the law makers to approve the motion and set firm closure targets for coal-fired power stations.
“There’s lots of talk about a dash for gas but in effect we’re in a dash for coal that’s completely unsustainable. The government must ensure it doesn’t continue,” he told the BBC.
Lord Smith said it is important that the UK developed its own reserves of shale gas, so long as gas power stations were able to store the resulting CO2 emissions in the future.
"If we lock ourselves into gas generation for the next 40 years without capturing the CO2 emissions, we will never meet our targets on climate change,” he said.
"At the current rate of progress we will miss our future carbon budgets."
The Environment Agency is an England-only non-departmental public body of the Department for Environment, Food and Rural Affairs.