The award-winning actress travelled from London to Stratford-upon-Avon to address a public inquiry into the future of the tiny Waterside Theatre.
The venue, a stone's throw from the Royal Shakespeare Company's three theatres, closed last year, and campaigners, including the district council, are fighting to stop plans by brewery chain J D Weatherspoon to turn it into a restaurant and bar.
She told the packed council chamber: "Once a theatre is gone, no matter how large or small, it is another brick removed from the foundations of our culture.
"Actors love their pubs as much as do any in the land - we probably love our theatres better - but a city-centre pub, on that corner, overlooking the river, does Stratford really need it? This much-loved theatre will be big in its uses, hosting concerts and conferences, and continuing to be a centre of excellence in education and a training ground for young people in all the performing arts."
She addressed the female government planning inspector directly asking: "Madam inspector, would you rather see your children or young relatives spend their free time in a pub, or would you rather they became involved in a youth drama, music, dance or art group?
"As we approach the millennium we are all busy reflecting on society's progress. What are we going to bequeath to the children of Stratford and their far-flung contemporaries?
"A cultural wasteland or another small jewel in this town's crown? Another pub or a cultural amenity which could change and enhance their lives?"
She urged the inspector to rule in favour of the district council in saving the theatre from "extinction" and said she hoped it would become a "further beacon of theatrical activity" in the town.
She criticised the Government for its lack of support for the arts saying: "I feel passionate about the future of the theatre in this country, and about this government - so fervent in opposition - and its failure to support the arts."
The actress, who sat down to rapturous applause, became involved with the campaign last year when she performed at the nearby Royal Shakespeare Theatre.
The inquiry was set up after Weatherspoon's lodged an appeal when the council blocked its application for permission to change the theatre.
Council planning officers had recommended granting permission, but the committee rejected it because it regarded the theatre as an important part of Stratford's cultural heritage that should be maintained.Reuse content