The investigation by art dealer Philip Mould, Fiona Bruce and the Fake or Fortune? team studied the provenance and detail of the Venetian view owned by Nick Hopkinson who inherited it from his great grandfather Meyer Spielman.
He grew up with the painting and had always loved it, but there was always a mystery surrounding who painted it.
On the back of the painting there are two labels from the Royal Academy – one names the artist as Marieschi and the other as Guardi.
Hopkinson long wondered who had actually painted it and contacted the Fake or Fortune? team for help.
Guardi and Marieschi were 18th century contemporaries of the most famous view painter of them all, Canaletto (1697-1768).
If it had been by Marieschi it could have been worth half a million pounds, if it was a Guardi it would be worth closer to £10m. However as a copyist, it is more likely to be valued at £20,000.
The investigation took the team to Italy, but further research in London revealed many of the family stories Hopkinson grew up with were not quite right.
During the programme the investigations raised the prospect the picture could actually be a later English copy.
However following a number of lines of inquiry, including detailed forensic investigations into the paint, the research into a ‘Firenze’ seal is believed to have proved the painting must have been in Italy as far back as the early 1800s.
But the fate of the picture was finally decided by specialist Charles Beddington, the Mayfair art dealer.
Beddington studied the research and the painting but concluded it didn't have the distinctive touch of either artist and was most likely to be by an English artist.
Hopkinson was crestfallen at the revelation but admits he still loves the painting.
The episode, the fourth in the eighth series of the BBC show, was broadcast on August 15 at 9pm.