McMullen & Sons, the Hertford-based brewer and pub owner, is going on sale for around £200m, according to the Sunday Times.

The sale is taking place because the trustees of the McMullen family trusts that own much of the company apparently believe the family should diversify.

McMullens, which owns 135 tied houses in Hertfordshire, Essex and London, is celebrating its 175th anniversary this year. Fergus McMullen, a great-great grandson of the company founder, Peter McMullen, recently took control of the brewing operations, and the company has just relaunched its flagship bitter, Country.

Its busiest tied house, the Nag's Head, in the centre of Covent Garden, London, is reckoned to be worth £10m on its own. The business turned over £47.3m in 2000, but the family is hoping a sale will fetch more than £200m because of its many freeholds.

The family, led by David McMullen, the company chairman, was number 526 in the Sunday Times Rich List of 2001, with an estimated fortune of £65m.

McMullens is said to be expecting interest from pub companies such as Pubmaster, as well as from independent brewers and property companies. Greene King, the brewer and pub group based in Bury St Edmunds, Suffolk, is also likely to be interested, according to the Sunday Times. Close Brothers, the investment bank, is expected to be appointed as adviser to the sale