Reading an extract in which Mr Powell said the "indigenous population found themselves strangers in their own country", he told Sky News presenter Dermot Murnaghan it was "true" about large parts of Britain.
He said he didn't know the origin of the passage - which also talked about the country being "changed beyond recognition" and women and children denied hospital beds and school places.
But told it was from the 1968 address warning of racial violence which led to Mr Powell being sacked from the Tory front bench and politically marginalised, he said the central premise was right.
"Is it? Well, what he was warning about is that if you have a large influx of people that changes an area beyond recognition, there is tension. That basic principle is right," he said.
Asked if Mr Powell "saw it coming", he replied: "Well no ... for different reasons and on a completely different scale. What we have had in the last 13 years is net four million extra migrants who have come to Britain so we are dealing with something on a scale that hitherto we couldn't have conceived."