More real ales - 2,000 different ones - are being brewed than at any time since 1971, according to the Campaign for Real Ale (Camra).
Real ale contains live yeast and improves in the cellar
In the past year, about 80 new breweries began producing real ale - twice as many as in the previous year, Camra's Good Beer Guide 2006 says.
Britain now has more small breweries per head than any other country.
Each of about 500 "micro breweries" across Britain produce up to 30,000 barrels of real ale every year.
That means one out of every five barrels of cask beer is now made by micro breweries - up from 14% in 2003.
The government's reduction in duty for small breweries has helped boost the number of new producers.
Yorkshire has 66 real ale breweries - the highest concentration in Britain.
The Society of Independent Brewers, which represents most of Britain's small breweries, reported a 12% sales increase for most members in its 2005 annual report.
Unlike lager, real ale contains live yeast and improves in the cellar.
Good Beer Guide 2006 editor Roger Protz said: "The giant national breweries will tell you people only want to drink lager but we know there are people who do not want to drink heavily hyped, over-promoted lager brands."
The guide, which lists 4,500 real ale pubs, says Britain's four biggest breweries "run massive factories dedicated to producing plastic beer".
"Volumes and profits, rather than consumer choice and quality, are their watchwords.
"Beer lovers are tired of over-hyped national brands and avoid like the plague the bland apologies for lager and the cold tasteless keg beers produced by the national giants.
"Beers with aroma and flavour are back in vogue and smaller breweries are rushing to meet the clamour from consumers."