Banksy’s largest and finest painting will go up for auction in October, but why has it been noticeably altered since it was last seen in public?

The newly renamed Devolved Parliament is expected to sell for an impressive £2 million, which would be a saleroom high for Banksy. It is the elusive street artist’s biggest known canvas painting and bears the satirical inscription: “Laugh now, but one day we’ll be in charge.”

“You paint 100 chimpanzees and they still call you a guerrilla artist,” commented Banksy when it was first unveiled in 2009.

Over the last ten years the 13-foot long painting has taken on new significance with the onset of Brexit. Alex Branczik, European head of contemporary art at Sotheby’s, said that “regardless of where you sit in the Brexit debate, there’s no doubt that this work is more pertinent now than it has ever been.”

300,000 visitors flocked to see the satirical painting when it was first put on display a decade ago at Bristol Museum & Art Gallery. Two years later, the painting was purchased by the current owner and has not been seen in public since.

Vigilant Banksy enthusiasts have now spotted unmistakable differences between the current painting and the original.

Two large overhanging chandeliers have totally disappeared, creating a far more gloomy and depressive mood to Parliament. Other smaller changes are also visible, including an upturned banana that now points downwards and the removal of a decorative piece of carving.

Confirming that it is still the same painting as the 2009 version, Sotheby’s acknowledged the alterations were made by Banksy himself.

“This work was first created in 2009. When, that same year, it was first exhibited at the Bristol Museum, it carried the title ‘Question Time.’ Since then, the painting has been reworked by the artist and more recently retitled,” said Sotheby’s in a statement.

But some dealers and buyers are disappointed by this explanation and are demanding further due diligence. Acoris Andipa, a London dealer who specializes in Banksy artwork, revealed “my clients need to be satisfied that a work is unique and that there are no other versions. It needs to be clarified.”

If Banksy did indeed make the changes in the painting, his motivations behind them are also shrouded in mystery. Does the gloomier tonality of the painting reflect his own outlook on Brexit? Is this all leading us towards another sensational stunt, like when his painting shredded itself at a Sotheby’s auction exactly one year ago?

Fortunately, we don’t have to wait too long for the answers; Sotheby’s will display the painting on 28 September before the auction at Bristol Museum’s Contemporary Art Evening on 3 October.