Taxation of estate income where residue is given to uk charities

Many years ago, I asked HMRC if it would agree to waive the need for the executors of an estate, which was given to UK charities, to report gross interest and dividends thus, saving having to submit figures, pay tax and then, issue R185s to the charities so that they could reclaim the tax. The answer I received was no! Can anyone tell me why they would have given me that decision! Due to pressure of work at the time, I just accepted it. As we know, even using the informal route to settle the tax can add some months to the administration period waiting for their letter and payment notice.