Dr Walter Mykura, a geologist died in a road smash in Edinburgh in May 1988, aged 62.
Last year, the royal brothers condemned the use of the photograph of Diana receiving medical attention in the Italian magazine Chi.
But Mr Lowther-Pinkerton said: "I'm afraid the fact that there's been a transgression in the past and people have objected to it strongly, as the princes did, doesn't mean that then you can wash your hands of it and it's fine to go on and do it - two wrongs don't make a right."
Julian Bellamy, head of Channel 4, confirmed that the pictures would still be used. He said: "We have weighed the princes' concerns against the legitimate public interest we believe there is in the subject of this documentary and in the still photography it includes."
Liberal Democrat culture, media and sport spokesman Don Foster defended Channel 4's stance.
"Most commentators who have actually seen the programme praise it for the sensitive way it deals with a very delicate issue," the MP said.
But the Tories condemned the inclusion of the pictures.
Hugo Swire, shadow culture, media and sport secretary, said: "This is an unprecedented intervention from the Royal Family and illustrates just how distressing the Princes find Channel 4's use of these images."
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