Never-before-seen picture claims to show elusive street artist Banksy at work on one of his most famous pieces on derelict pub wall

He is wearing a high-vis jacket but he isn't attracting much attention. And that's just the way he likes it.

For a never-before-seen picture shows elusive street artist Banksy at work on one of his most famous pieces – a giant white rat daubed on to Liverpool's derelict White Horse pub, The Daily Mail claims.

It is the first photograph to identify Banksy at work, and suggests he is indeed former Bristol public schoolboy Robin Gunningham, first unmasked by The Mail on Sunday in 2008.

Since the revelation, rival theories have continued to abound. Some claim that Robert Del Naja, of Bristol pop group Massive Attack, is the real Banksy, and last week a picture taken in Tel Aviv led to renewed speculation. It turned out to be a photo of a 45-year-old Anglo-Israeli graffiti artist called James Ame.

But a new book called Stealing Banksy? has concluded that The Mail on Sunday was right all along.

It is written by Tony Baxter of the Sincura Group, which has rescued and restored several Banksy murals, and it includes the picture of the artist painting his White Rat in 2004.

It was taken by photographer Christopher Wilson, who said: "I knew Liverpool was going to be regenerated so I thought it would be a good idea to make a record of the decayed buildings beforehand. So, I wandered around the town centre, taking photographs.

"There is no way that anybody can ignore the evidence now."

The Mail on Sunday's 2008 scoop came after a year-long investigation in which we spoke to dozens of people associated with Gunningham, a former Bristol Cathedral School pupil now married to former Labour researcher Joy Millward.

Banksy did not issue an absolute denial at the time, issuing a statement on his website saying: "I am unable to comment on who may or may not be Banksy, but anyone described as being "good at drawing" doesn't sound like Banksy to me."

Last year, geographic profiling, more often used to catch criminals or track the spread of disease, found Gunningham was "the only serious suspect".

Today, Banksy is said to be worth about $38 million.

The Liverpool giant rat was removed from the pub when it was refurbished in 2014.

Earlier this year it was sold with four other Banksy pieces removed from walls in Liverpool for a reported $7.4 million to an anonymous Qatari buyer.

Stealing Banksy? is available from stealingbanksy.com.