LONDON (Dow Jones)--Heron International Ltd., a private property company owned by magnate Gerald Ronson, is an early frontrunner to buy Tower 42, the tallest office building in the City of London, the Sunday Times reports without citing sources. The 600 foot skyscraper was put up for sale by Hermes, the property fund management arm of the BT Group PLC (BT.A.LN) pension fund, and fund manager BlackRock, in April. The building, which produces rental income of GBP20 million a year, is expected to fetch about GBP300 million, the newspaper says. Competing bidders include U.S. private equity fund Blackstone Group L.P., it adds. The sale will include five low-rise buildings next to the tower, including the Grade-I listed Gibson banking hall, making it one of the biggest freehold properties in the City, it says. A spokeswoman for Heron declined to comment on whether the group is bidding for the tower, but said it remains actively looking for acquisitions. Newspaper Web site: www.timesonline.co.uk -London Bureau, Dow Jones Newswires; +44 (0)20 7842 9320 (END) Dow Jones Newswires June 20, 2010 09:05 ET (13:05 GMT)