The Department of Energy and Climate Change had consistently maintained that the cost to the public purse of launching two appeal attempts was approximately £66,000.
But today, Barker admitted that the final cost was still unknown but confirmed that the legal bill so far was now £83,870.
And it is believed the total amount paid by the department will top £400,000 after it was ordered by the Supreme Court to pay the costs of the successful litigants Solarcentury, Friends of the Earth and HomeSun.
Mr Barker said the costs of the three organisations had not yet been assessed but it is known that each legal team racked up a near six-figure bill during the protracted court battle.
An original decision to reject a call for a judicial review was successfully overturned by the three companies last December.
Following a two-day hearing, a High Court judge ruled the then secretary of state for energy, Chris Huhne, had acted unlawfully by reducing the subsidy for new solar PV installations ten days before a consultation exercise was completed.
The Court of Appeal refused Government attempts to overturn the ruling and denied leave to appeal the decision to the Supreme Court.
A direct application by DECC’s legal team to the highest court in the land also failed meaning the new cut off date for reduced Feed-in Tariff payments was a contingency deadline of March 3.
Mr Barker also said DECC had not estimated its potential liability for loss of income following the Supreme Court ruling, adding: “The Government have made no such estimate, as it does not accept that it has any such liability.”