Prince William and Kate Middleton remain the most popular royals, according to YouGov figures quoted in the report.
Around 72 to 74 percent of Britons have a positive opinion of them. These ratings have stayed mostly the same over the past few years.
Princess Anne is also popular, with 68 percent of the public viewing her positively.
The report says the survey came after Prince Harry and Meghan Markle returned to Britain in August. Their ratings, however, have fallen since July.
Harry is viewed positively by 29 percent of Britons, down four percentage points. Meanwhile, 60 percent have a negative opinion of him.
For Meghan, 20 percent have a positive opinion, while 68 percent view her negatively. Her negative rating has risen by three percentage points since the summer.
This gives Meghan an overall popularity score of minus 48. That means negative views outweigh positive views by 48 percentage points. The report says this is her lowest score since tracking began.
King Charles still has more positive than negative ratings, although his popularity has also dropped.
According to the figures quoted, 58 percent of Britons view him positively, down four percentage points since July. The report describes this as his lowest positive rating since becoming King.
Meanwhile, 34 percent view Charles negatively, up three percentage points. This equals the highest negative rating recorded during his reign.
