Alan Bennett's new play People has opened at the National Theatre, in which the playwright takes a swipe at the National Trust.
Bennett revealed last week that People was inspired by his sense of unease while visiting a National Trust house.
Set in a crumbling stately home, the play stars Frances de la Tour as the impoverished owner resisting its sale to the charity.
Critics have described the play as "provocative fun".
Michael Billington in The Guardian says the play raises the "intriguing prospect of a running war" between two NTs: the National Theatre and the National Trust.
The National Trust told the BBC on Thursday that it was "flattered" to be woven into Bennett's play, but it was "not quite the organisation he thinks we are".
People, directed by Nicholas Hytner, sees de la Tour in her third new Bennett play at the National following The History Boys and The Habit of Art.
She plays ex-model and aristocrat Dorothy Stacpoole, who faces the choice of auctioning off the house, letting the National Trust open it to visitors, or selling it to a shady consortium.
Dorothy describes the National Trust as a "pretend England... so decent, so worthy, so dull".
In the meantime she allows the house to be used as the set for a porn film.
"Bennett's play feels less like a class comedy than an old man's rage against the sterility of today's cautious, over-organised society, where all boxes must be computer-ticked, and all human spirit and oddity processed away," said Ismene Brown in her review for The Arts Desk.
"Upending his cuddly reputation, he gives the poor old National Trust a really bloody nose."
A National Trust spokesperson said: "We are looking forward to seeing Alan Bennett's play and of course it is flattering to be woven into it, but we are not quite the organisation he thinks we are!
"The National Trust has changed a lot over recent years to reach out and engage with as wide an audience as possible across our houses, gardens, coast and countryside. We want everyone to love the special places we look after.
"We know we can't always please everyone but we do feel hugely confident we are on the right lines with 4 million members and 17 million paying visits, and the goodwill and enthusiasm of 67,000 volunteers, along with more than 100 million pounds a year spent on conservation."
In his introduction to the play, Bennett writes: "Some plays seem to start with an itch, an irritation, something one can't solve or a feeling one can't locate. With People it was a sense of unease when going round a National Trust house and being required to buy into the role of reverential visitor."
He goes on express his dislike of being fed information about the room or its furniture by National Trust guides.
"Even when I am interested but want to be left alone with the pictures or whatever, I have learned not to show too much interest as this invariably fetches the guide over, wanting to share his or her expertise."
"At 78, Alan Bennett has lost little of his mischievous wit and sense of the ridiculous," says Charles Spencer in his four-star review in The Telegraph. "His eagerly awaited new comedy, People, may not be out of the top drawer of his work, lacking the emotional depth and sly subtlety of his best writing, but it is entertaining, funny and touching."
In The Mail, Quentin Letts was more reserved. "Mr Bennett's text has strong moments - there is a stinging speech about how the Trust likes to 'maximise our percentage footfall' as a 'growth organisation' - but the dramatic execution lacks political ruthlessness and the lines are delivered without subtlety."
He added: "People has a good theme but the production doesn't half plod in places."
The play, at the Lyttelton theatre until next February, includes a running joke about the Stacpoole home's collection of chamber pots which still contain the urine of famous visitors over the decades.
The National Trust statement added: "A Demos survey at the end of last year showed that the National Trust and Shakespeare were the top two sources of pride in being British.
"On top of that, we also look after over 550 chamber pots, though unfortunately most are empty."