The Energy Secretary Amber Rudd has been accused by Labour of misleading MPs about meeting mandatory EU energy targets on renewable power.
A leaked letter from Ms Rudd to cabinet colleagues in October warns of a shortfall in the UK's clean power targets to 2020 of about 25%.
Ms Rudd, who faces the Energy Select Committee later, earlier told the Commons the UK was meeting its targets.
The government told the BBC it still aimed to hit the energy goals.
Opposition MPs say they have been deliberately misled - and accuse the government of a doctrinaire aversion to wind and solar power.
In September, Ms Rudd told the Commons the renewables budget had to be reined in because it was "way overspent".
It did not matter, she told MPs, because "we're still meeting our renewables targets".
However, the following month she sent a confidential note to cabinet colleagues with a very different tone.
In it, she warned of a shortfall in renewable energy for 2020 approaching 25%. This was not public knowledge, she said.
She said if the gap were not plugged, it would potentially trigger huge fines from the EU and legal action in the UK itself.
A spokesman for the Department of Energy and Climate Change (DECC) said this proved Ms Rudd had intended to meet the UK's renewables targets.
But Labour has accused ministers of bringing the UK into international disrepute as the world approaches the big UN climate summit at the end of the month.
Lisa Nandy, Labour's shadow energy secretary said: "At the very same time the energy secretary is telling her colleagues in private we're not on course to meet our legal target on clean energy, she is cutting wind and solar schemes that could help us to meet it. It beggars belief."
A new assessment by BBC News suggests almost all of the energy policy changes made by the chancellor since the election are likely to push up CO2 emissions.
And the UN's chief environment scientist has expressed alarm at the UK's domestic energy policies.
Ms Rudd acknowledged in her leaked letter that getting more heating from biogas - produced from waste - would help the UK meet its targets.
Yet companies that have invested in biogas are livid the chancellor has cut the subsidy they were promised.
One solution Ms Rudd proposes is to buy renewables "credits" from other nations that have achieved their EU energy targets.
Another is to try to negotiate the UK's renewables targets down.
Daisy Sands, from Greenpeace, said: "This is hugely shocking.
"The government is planning on cutting support for the solar and wind subsidies in the name of affordability.
"This policy makes no environmental or economic sense, as the UK is losing jobs and affordable clean, renewable energy sources."
Follow Roger on Twitter: @rharrabin