The family office of South African billionaire Nathan Kirsh is in exclusive negotiations to buy the former NatWest headquarters, in the heart of the London, after bidding 285 million pounds for the skyscraper, the Times reported on Friday.

The newspaper said, without citing a source, Kirsh's bid for Britain's tallest building is thought to have outweighed those of rival contenders by at least 10 million pounds.

He beat off the London-focussed Exemplar Properties and the private equity firm Doughty Hanson, according to the article.

The 2.2 acre estate was put up for sale by its joint owners, BlackRock UK Property Fund and LaSalle Investment Management, with a 290 million pounds price tag.

In addition to the skyscraper, which was renamed Tower 42 when NatWest Bank moved out, the site includes four other adjacent properties. Jones Lang LaSalle, the property adviser, conducted the sale.

(Reporting by Stephen Mangan; Editing by Richard Chang)