Portugal's government put 85 works by Spanish surrealist artist Joan Miro up for auction .

The collection became public property when the Portuguese Bank of Business was nationalised in 2008.

Christie's auction house in London, which is handling the two-day sale, described the collection as "one of the most extensive and impressive offerings of works by the artist ever to come to auction."

The sell-off has stirred controversy, with some Portuguese citizens demanding the collection be publicly exhibited rather than sold.

But just hours before the auction was due to start, a Lisbon judge turned down the opposition Socialist Party's appeal to stop the sale.

The government says the bailed-out country's austerity drive has left it short of cash and the Miro collection is not one of its priorities.

Portugal received a €78 billion (£64bn) bailout in 2011 to spare it from bankruptcy and has been subject to swingeing conditions ever since.

Other countries have also offloaded their failed banks' art collections.

The collapse of Lehman Brothers, the Bank of Ireland and South Korean savings banks have in recent years brought to market several works by big-name artists.

Like elsewhere, the Portuguese auction will barely make a dent. Christie's has estimated the Miro collection at around €36 million (£30m) while the 2008 collapse of the bank left taxpayers at least £2.8bn out of pocket.

The Lisbon trial of 15 people for the bank's collapse amid allegations of corruption, fraud and mismanagement has been running for three years.