Forget dressing smart or casual for the opera. If you dress up as a fox, badger, bat or indeed any woodland creature at the UK’s newest opera house then you may well get a free seat in a box.

Animals have been sensitively moved during the construction of Grange Park Opera’s new theatre, due to open in June, so its founder and chief executive, Wasfi Kani, has decided to create a dedicated box for woodland animals.

“We did displace some bats and badgers,” said Kani. “We had to find them all alternative accommodation … they had to shove up a bit, just shove up a bit.”

Would-be furry animals need to book in advance and Kani said she would be the judge as to whether costumes are good enough.

It is one of several possibly eccentric elements in a £10m development taking shape in the grounds of a beautiful but dilapidated stately pile unexpectedly inherited by the former University Challenge presenter Bamber Gascoigne on the death of his great-aunt, Mary, Duchess of Roxburghe.

Other touches include a planned model railway in the foyer; a balcony for four trumpeters who will summon opera audiences from their picnics; and the entombment of the duchess’s ashes underneath the first violins in the orchestra pit.

“I don’t think she particularly liked music,” admitted Kani. “But she has got a lot coming!”

Then there are the planned doors, which will be copies of those at the Pantheon in Rome. “I thought why not?” said Kani. “I like a bit of classical. Martin Smith, our builder, can do anything.”

Kani revealed her plans while taking the Guardian on a tour of the five-storey, 700-seat theatre in the woods, still something of a building site.

It is an almost crazily ambitious arts project, interesting on many levels. It emerged from an acrimonious dispute, has taken place in a remarkably short space of time and is only happening because of what is a wonderful story involving Gascoigne.

To his immense surprise Gascoigne was left West Horsley Place, a 16th-century manor house in Surrey, after the death in 2014 of his great-aunt, one of the last survivors of a vanished aristocratic age.

Gascoigne, who had enjoyed happy lunches there but had never even set foot upstairs, was delighted but taken aback, soon discovering that the house, for all its beauty, needed extensive restoration. He told the Guardian at the time: “People who know about houses say ‘I do sympathise with you’. They say ‘thank God it isn’t me’.”

A sale was held of its many wondrous contents, from an Asprey breakfast-in-bed tray to monogrammed china, raising £8.8m, money which is being used to secure the house’s future.

At the same time Kani, as she puts it, was being “turfed out” of the Grange, an uninhabited neoclassical mansion in Hampshire owned by the Baring family which had been, since 1998, the home for her summer festival company Grange Park Opera.

Kani needed a new venue and was alerted to the newspaper stories about Gascoigne. They met in May 2015 and she discovered she was pushing at an open door, with Gascoigne suggesting a rather beautiful wood at the back of the house.

That set in motion a plan for an entirely new building, to be known as the “theatre in the woods”. “We had to start building quickly because I had a massive number of contracts for 2017,” said Kani. “I booked [Die] Walküre five years ago … I had to have this festival.”

There have been challenges, not least getting planning permission to build in the greenbelt as well as raise the £10m needed. “But we did it and look at it … it is amazing.”

The first Grange Park Opera festival season at its new home will open on 8 June with Tosca, starring the tenor Joseph Calleja, followed by Jenufa, Die Walküre and a concert featuring Bryn Terfel and prima ballerina Zenaida Yanowsky.

Wasfi said she also hopes to attract dance companies such as English National Ballet, Ballet Boyz and Matthew Bourne’s company New Adventures.