Sir Keir Starmer said Prince William could have “gone further” in his comments about slavery during his visit to Jamaica.
The Labour leader also said the couple’s decision to be driven around in a 1953 Land Rover “harked of the past”.
He made his criticisms in an interview on LBC radio.
The Duke of Cambridge used a speech in Kingston last week to condemn Britain’s “abhorrent” history of slavery but stopped short of a full apology.
The Jamaican government was said to be “incredibly disappointed” that he failed to say sorry.
Asked for his response to the prince’s speech, Starmer told LBC: “He could have gone further but, again, it’s a difficult one. I think that he may go further in the future.”
Asked if the trip - which has been widely criticised as a PR disaster - was a failure, the Labour leader replied: “No I don’t think it was.
“William and Kate went on an important trip with important messages including messages about the changing nature of the Commonwealth going forward and that is difficult, but it’s very easy to sit here and criticise.”
Presenter Nick Ferrari asked him if it was wise for the couple to be driven around in an open-top 1953 Land Rover that seemed “reminiscent of the empire”.
Starmer replied: “Having just said I don’t want to criticise, I have to say that I found that a bit odd.
“In a sense what William and Kate were doing, which I applaud, is saying we’re looking to the future.
“But that all harked of the past so I didn’t quite see how that actually fit that well with the aim of their trip.”