Antiques Roadshow expert Rupert Maas was forced to apologise to a guest after giving a false valuation.

During the latest episode of the BBC show, one guest took along a painting to find out how much it was really worth. Rupert was on hand to study the item that was believed to have been created by Sir Peter Lely - a renowned Dutch artist. He went on to become Charles II's Principal Painter in Ordinary and his works carry huge price tags.

The proud owner told Rupert: "We know it was bought in auction in London in the 1850s by the brother of my great, great grandfather who was Sir Charles Forbes. Various artefacts have been passed down and we've been fortunate enough to end up with this fella hanging on our wall."

Expert Rupert said: "It looks to me like it's got something to do with Sir Peter Lely - the famous 17th century portrait painter. The question is, is it by Lely?" He added: "The catalogue of 1845 you've just shown me says Lely doesn't it? Quite clearly." However, Rupert pointed out there are issues with artwork descriptions from that time.

"The thing about Lely, the great portrait painter that he was, is that when he died he left hundreds of unfinished portraits and versions of portraits already done," the expert explained. "His students and studio assistants finished them really quickly, and sold them all so that his entire estate including his collection of old masters made something like £30,000 in the 17th century - a massive amount of money, he was so popular. It effectively flooded the market with versions of his pictures done by lesser hands, the question is, is it one of those?"

After taking a closer look, Rupert continued: "Sorry, but I think, I'm afraid this is a shadow of a dream. In other words, it's not even by a studio citizen, I think it's a much later copy. There's something about the reduced scale - of course it should be massive - makes it look more domestic. Something about the frankly Victorian idea of a 17th century frame, it's been copied."

He pointed out: "The colours are slightly gaudier than you'd expect, a little bit of clunkiness in the drawing of the hand. And then put on top of that brown finish which is quite deliberately antiquing it, I think what we're looking at is a 19th century copy. I'm sorry, but it might even have been new when it was in this catalogue."

Giving the all important valuation, Rupert teased: "So if it was an original Lely, it would be pretty well around £1 million." He then tld the guest: "But as it is, it's probably worth around I don't know, £600 - but decorative and nice enough! I'm sorry to let you down." The disappointed guest responded: "That's alright. Thank you very much."