A YouGov poll commissioned by the Press Association found that 36 per cent of the British public think Charles has been beneficial to the monarchy, compared to 60 per cent in 2013.
More than a quarter – 27 per cent – think the longest-serving heir to the throne has had a negative impact on the royals, in contrast to just 15 per cent four years ago.
The research also showed that only 14 per cent of the British public want the Duchess of Cornwall to become Queen when Charles is King.
Most – 39 per cent – think she should take the title of Princess Consort instead, while almost a third of Britons – 30 per cent – believe she should not have any title at all.
Royal commentator Penny Junor suggested the public has still not forgiven the Prince for the breakdown of his marriage to Diana, and his standing had fallen because of the publicity surrounding the anniversary.
She expressed surprise at the findings, saying: “We’ve moved on 20 years. Charles’s reputation, I thought, was completely rehabilitated. He’s become a much happier, more relaxed and more confident Prince of Wales and I thought much more popular as a result.”
The author of the Camilla biography The Duchess: The Untold Story described Charles as “the most extraordinary Prince of Wales”, adding: “I think he has been visionary over the years, the issues he’s tackled have all become mainstream thinking.”
But she said: “He gets a hard time because his marriage failed. He’s never been forgiven for that - because Diana blamed him and he never ever said a word. He’s never explained what went on in his marriage. His view has always been that history will judge him. He knows that he did all he could to try and make his marriage work and he failed.”
The poll follows surveys by national newspapers which also found unfavourable public opinions towards Charles and Camilla.
A Sunday Express poll found 67 per cent did not support the Duchess taking the title of Queen when her husband becomes King. An ICM poll for the Sun revealed 51 per cent wanted the Duke of Cambridge to be the next monarch, while only 22 per cent surveyed said Charles.