The deal will make Admiral Tavern the third largest pub operator in the UK, leap-frogging Marston's and Greene King, according to a report in today's Times newspaper.
Admiral already has 1,800 pubs and is expected to splash out £330m on the bottom-end of Punch's estate.
Operators have been rushing to sell some of their assets with the impending smoking ban in England set to hit smaller, wet-led pubs.
Enterprise sold its 137-strong Scottish estate to Retail & Licensed Properties, a division of Robert Tchenguiz's investment vehicle R20 last year, while Marston's has around 300 properties on the market for sale.
Punch is expected to join the FTSE 100 after cigarette company Gallaher was acquired by Japan Tobacco.
Punch has see shares rise by 48% in the past year and has a market cap of £3.43bn.
Pub company Mitchells & Butlers is also waiting in the ings to join the FTSE 100.
By Christopher Walton
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