It is as Irish as shamrock and the Blarney Stone, but a pint of Guinness is falling out of favour in its home country.

The iconic drink, which has been brewed in Dublin for the last 250 years, is suffering a severe downturn in sales, the company admitted yesterday.

Diageo, the UK drinks giant that owns Guinness, said volumes of the stout fell by 10 per cent in Ireland in the last six months as increasing numbers of drinkers die off.

Paul Walsh, Diageo's chief executive, said: "What is happening in Ireland is that 50 to 60 year olds who were going out five or six nights a week and drinking five or six pints are being replaced by a younger consumer, who goes out three nights a week and drinks two to three pints."

Drinks experts think the problems could run deeper than a shift in demographics.

Roger Protz, the author of the Good Beer Guide, said: "Guinness is not the beer it used to be 20 or 30 years ago in my view. It is now thinner and has a rather unpleasant bitterness."

The company insists it has not changed the "taste profile" of Guinness in recent years and said it was still the favourite drink in the pubs of Dublin, Galway and Kilkenny, outselling nearest competitor Heineken by two to one.

The Catholic bishops of Ireland have added to the company's woes, calling for their flock to give up the black stuff for Lent - meaning that drinkers would have to stay dry on St Patrick's Day.