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The sole survivor of the car crash which killed Princess Diana said Dodi Al Fayed had insisted on the ill-fated decoy plan to dodge waiting paparazzi.
Trevor Rees said he had had reservations about Mr Al Fayed's plan to sneak out of the Ritz Hotel.
He suffered serious head injuries and made a good recovery but has said he has little memory of events which led up to Diana and Mr Al Fayed's deaths.
Giving evidence at their inquest, he denied being part of a murder cover-up.

Mr Rees, who was known as Rees-Jones at the time of the crash on 31 August 1997, told the jury he went along with the plan because Dodi had talked about leaving the Paris hotel with no security.

Waiting photographers
The jury has heard the decoy plan involved two cars, including a Mercedes with an official driver, waiting at the front of the hotel opposite a crowd of photographers.
The couple would then leave in a third car from the rear of the hotel, driven by Henri Paul, who was not an official driver.

The plan failed as there were already photographers waiting at the back and it meant the car left without a trained driver and a decoy car.
Mr Rees said he could not remember if Mr Al Fayed or Mr Paul first told him of the plan but was sure the idea had come from the former.

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Please look at the sentences in bold.
Diana said Dody Al Fayed had insisted on the ill-fated ...
Trevor Rees said he had had reservations about Mr Al Fayed's plan to ...
The above are past perfect constructions.
Is it imperative to write past perfect in the given context?
What is wrong with the following:
Diana said Dody Al Fayed insisted on the ill-fated ...

Trevor Rees said he had reservations about Mr Al Fayed's plan to ...
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>Diana said Dody Al Fayed had insisted on the ill-fated ...

This is totally out of context and wrong. It's "The whole survivor/Trevor Rees" who said, not Diana.

And no, you can't use the simple past in either of them: "said" is much later than the events of the accident, which are reported by him.

Again, learn from the editors, they know good English.
Comments  
I think it's just the writer's way of showing time and sequence of events.

Diana said Dody Al Fayed had insisted on the ill-fated ...

Everyone is trying to figure out what and how this tragedy happened.

The past perfect tense can help put events in order.

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So the simple past is not wrong here.
 Marius Hancu's reply was promoted to an answer.