The Stig, Top Gear's mystery racing ace, has revealed his identity to the owners of a photo gallery in Bristol – but has made them sign an oath of secrecy.

When a stranger walked into the C2 Gallery in Clifton, he told father and son owners Roger and Simon Whitehead that he was a BBC marketing executive.

They discussed making 200 high quality prints of a picture of The Stig posing on the Salt Lake desert in America.

But as the negotiations for production and sale of the signed Stig pictures went on, the man revealed he actually was the white-helmeted hero of the Top Gear circuit.

And he insisted the pair signed a confidentiality agreement promising never to divulge his true identity.

"I suppose it could be a wind up – after all, we have no way of knowing for sure that this man really is The Stig," said retired catering company executive Roger.

"The man we are dealing with is not a household name like Lewis Hamilton or anyone like that – but I have checked out his background and he certainly is a man with the right credentials to be The Stig.

"He is definitely capable of doing The Stig's job and we have no reason to disbelieve that this actually is him.

"I was gobsmacked when he told us who he really is. We had no idea. Why he should have chosen to come to a gallery in Bristol I don't know – although we are very close to the BBC studios in Clifton and we see a lot of producers around here."

The Stig approached Roger and Simon, a Falmouth college graduate son and professional photographer who runs the gallery, to make the prints last September.

"This guy appeared and said he had a print he wanted us to mount for him," said Roger.

"He had seen pictures in our gallery and liked the contemporary look we give to images.

"He said he was from BBC marketing. We sat down with him and priced the job up. It was for a limited edition run of the picture, each of which would be personally signed by The Stig.

"We asked him who had the copyright on the photograph and he said he did, and we told him he would have to sign a document to verify that.

"We agreed to produce numbers one and two of the limited edition and they have been up in the gallery and have been sold.

"After our discussions with this man he said, "I need you to agree to this confidentiality agreement", and he produced a sheet of typed paper and asked us to sign that we would not reveal his identity.

"We asked who he was and he told us he was The Stig."

Roger said that since producing the first two prints, they have had a lot of trouble getting in touch with The Stig so he can call at the gallery and sign more.

"He is obviously very successful in what he does because he is so hard to get hold of," said Roger.

"He sometimes rings and apologises that he hasn't got back to us."

The Stig photographs are produced to order in a choice of three sizes for clients – many of whom are bosses of car dealerships and want the images to go on their showroom walls.

A 20in by 30in mounted print of the picture sells at £318.09 in the Bristol gallery.