Auction house Christie's was left baffled over a painting depicting a woman on a hot summer's day in seaside street.

A Fete Day At Brighton is one of 19th-Century French artist James Jacques Joseph Tissot's most admired works, and could fetch up to £2.8 million when it goes under the hammer next month.

But two weeks ago, Christie's appealed to readers of The Argus for help in identifying the street in the painting.

Ken Fines, borough planning officer of Brighton from 1974 to 1983, is convinced he has solved the riddle.

Mr Fines said the answer could only be West Street.

The painting depicts Tissot's girlfriend Kathleen Newton in an elaborate dress, strolling along a Brighton street leading up from the sea.

The couple caused a scandal in London by living together because Mrs Newton was a divorcee.

They spent much of their time at resorts such as Brighton where questions were not asked about the absence of a wedding ring.

The painting captures Mrs Newton walking among the bustle, colour and festivities of the town holiday.

Mr Fines, 82, of Northease Drive, Hove, and his daughter Susan Barnbrook, have certainly done their research.

As a collector of old documents, Mr Fines even has a 1:2500 scale Ordnance Survey map of Brighton dated 1877.

This sits right in the middle of the 1875 to 1878 period during which A Fete Day At Brighton is thought to have been painted.

Mr Fines has sent Christie's a copy of the map with a red X marking the spot where he believes Mrs Newton to be in the painting.

He said: "The setting can only be the top of West Street. What clinches it is that to be at the top of West Street, close to where there is a change of gradient, there needs to be a road turning off to the left, and there is."

"Just behind Kathleen, one can see the kerb curving round and a gap in the street frontage. This is Duke Street, which leads down into the Old Town bounded by West Street, North Street, East Street and the seafront."

Mr Fines, recently voted into The Argus' top ten heroes of Sussex for his work as director of the Greater Brighton Structure Plan, is not a man to be taken lightly.

Three years ago, his book, A History Of Brighton And Hove, was published.

A Fete Day At Brighton will be auctioned by Christie's at the Rockefeller Center in New York on October 26.

A spokesman for Christie's said Mr Fine's research into the painting could be included in the cataloguing.

He said: "It's a great help to have local knowledge. If Ken Fines knows Brighton like the back of his hand, that can only be a good thing in determining the location of the street."