Complex sentence: The tower was built as council housing but 14 of the flats had been bought under the Right to Buy policy; these were occupied by leaseholders or were privately rented out by them on the open market.
Split into simpler sentences: The tower was built as council housing, but 14 of the flats had been bought under the Right to Buy policy. These were occupied by leaseholders, or were privately rented out by them on the open market.