The Prado museum in Madrid is at the centre of political and artistic row over its purchase of a Velazquez painting for €23m (£16m).
Critics say it could have bought a finer Goya for less money.
The Prado yesterday hailed its purchase this week of The Pope's Barber as one of its most important acquisitions in decades, saying it had bought a key work never before been in the artist's homeland.
It shows a humble man, portrayed with dignity and wisdom, in a style perfected by Velazquez at the height of his powers.
The painting has been in private hands outside Spain since Velazquez painted it on a visit to Italy between 1649 and 1651. An American collector recently put it up for sale.
But critics say the museum missed the opportunity to buy Celestina and the Girl on the Balcony, the finest Goya canvas still in private hands.
The Prado dismissed suggestions that the Velazquez was inferior. Officials said they were never offered the Goya, and that there was never any question that they favoured one over the other.
Goya's painting shows a young prostitute leaning over a balcony, with her procuress standing in the background. It was painted between 1808 and 1812 during the Peninsular War when the artist portrayed many aspects of Spanish low-life, reflecting his bitterness and disillusion during a period of anarchy and violence. The work recently changed hands between private Spanish collectors for €18m.
Press reports this week said the Ministry of Culture, which controls the Prado, showed no interest in the Goya when it was put up for sale in Madrid even though the gallery had right of refusal for such an important work.
The painting was sold through Christie's in Madrid by Bartolome March, of a leading banking dynasty, to Alicia Koplowitz, an enthusiastic collector said to be the richest woman in Spain.
Amparo Valcarce, the opposition Socialist Culture spokeswoman, said she would demand an explanation in Parliament for the Culture Ministry's handling of the Goya sale.
A Prado spokeswoman said yesterday the museum had not been told the Goya was on offer.
By contrast, it was so eager to acquire the Velazquez that its director, Eduardo Serra, formerly the Defence Minister in Jose Maria Aznar's government, shipped The Pope's Barber over from New York before the sale, to offer Mr Aznar a private view and secure the Prime Minister's approval of the purchase, ABC newspaper reported.
The Prado says the two transactions cannot be compared, since the Goya "remains in Spain", while the Velazquez is acquired from overseas to enrich the national collection.
Jonathan Brown, the world's leading expert on Velazquez, said: "The portrait is one of the few remaining from Velazquez's second visit to Rome. The technique is miraculous, with almost transparent colours showing the canvas beneath. It fills the last gap in the Prado's Velazquez collection."
But commentators see darker political forces at work. The influential El Mundo columnist Francisco Umbral denounced the affair as reflecting a ruling climate of Catholic moralism. "It's a return to the Franco mentality of censoring Goya, the chronicler of black Spain ... in favour of the court painter Velazquez who celebrates Spain's palace life," he wrote.
Spain's rulers were so gripped by "Catholic flu", he added, that they were offended by a painting of a prostitute plying her trade.Reuse content