Halliday & Matthiessen (2014: 703):
In the realm of propositions, the line between explicitly objective propositions and modal assessment seems to disappear. Forms such as it is said that, it is rumoured that serve as assessments of the nature of the evidence for a proposition: it is, as it were, represented as being projected by somebody other than the speaker (thus it is said and they say are very close in meaning); the projection thus serves as a device enabling speakers to distance themselves from the proposition. For example:
||| Of Samuel it is said || that when he asked the people || to bear witness || that he had not taken anything of theirs || the people said || that they were witnesses. |||||| It is said || that television keeps people at home. ||| But you, at any rate, have proved that wrong. ||| And they say, too, || that television makes its appeal to those of lesser intelligence. |||||| Furthermore, it is claimed, || there are no known connections between the languages of the Old World and those of the Americas. |||