Buyout firm Exponent emerges as frontrunner for Big Bus Tours - sources

(Adds detail on deal, company)

By Freya Berry and Anjuli Davies

LONDON, Feb 6 (Reuters) - UK private equity firm Exponent has emerged as the frontrunner to buy open-top sightseeing company Big Bus Tours, two sources familiar with the matter said on Friday.

Reuters reported last year that the owners of the company, which is partially family-backed, had hired JP Morgan to run a sale potentially worth up to 500 million pounds ($762 million).

Exponent (NasdaqGS: EXPO - news) , which sold UK rail ticket website thetrainline.com to KKR in January, is poised to buy the company, and a deal is expected to be announced soon but is not yet certain, the sources said.

Big Bus Tours' burgundy and cream-coloured open-top buses are a familiar sight around London, and the company has quickly expanded across three continents and 17 cities, including Shanghai, New York and Dubai.

The business was formed in 2011 by the merger of London-based The Big Bus Company (TBBC) and French peer Les Cars Rouges. Shareholders include the Maybury family, which founded TBBC in 1991 and Abu Dhabi-based Al Fahim Group, which acquired 30 percent of TBBC in 2000.

Exponent and JP Morgan declined to comment. Big Bus Tours and Al Fahim Group were not immediately available to comment.

($1 = 0.6560 British Pounds) (Reporting By Freya Berry and Anjuli Davies; editing by Pamela Barbaglia and Elaine Hardcastle)