The number of people who believe the Prince of Wales has made a positive contribution to the Royal Family has fallen in the run-up to the 20th anniversary of Princess Diana's death.

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 Brits - 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.

The Press Association-commissioned poll follows surveys by national newspapers which also found unfavourable public opinions towards Charles and Camilla.