At London’s Jerwood Space, Garsington Opera rehearsals are in full swing. I am watching the men’s chorus being drilled for Fidelio, and can’t help thinking that the glorious sound they are making bodes well for the forthcoming season.

In less than two weeks, the action will have moved from this rather functional space to the altogether more glorified setting of Garsington Manor, as the 20th anniversary season gets under way. It was in 1989, seven years after moving into the small 17th-century manor house, that Leonard Ingrams invited Opera 80 to put on a couple of performances of The Marriage of Figaro in the wonderful Italian-style gardens.

From that humble seed grew an opera season that has become one of the most respected summer opera festivals in the country.

Much of the success of Garsington stems from its romantic, balmy atmosphere, of which Virginia Woolf once wrote: “Is the air ever normal at Garsington? No, I think even the sky is done up in pale yellow silk.” The Wall Street Journal has described it as “the most idyllic setting for opera you will ever experience”.

The fact that the festival has endured for 20 years is down to the high standards set by Leonard Ingrams, who put an increasingly professional gloss on the productions.

He also ensured that Garsington Opera had its own distinctive character, with a twin emphasis on seeking out unknown operas and giving opportunities to promising young singers.

The company continued his legacy after his untimely death in 2005, aged 64, and now also has a thriving education programme that introduces local schoolchildren to the joys of opera.

Of course, Garsington, like other country house opera festivals, owes much to the grandfather of them all, Glyndebourne, which celebrates its 75th anniversary this year.

So, it is fitting that the man invited to take on Leonard Ingrams’s mantle in 2006 was someone who could list Glyndebourne among the many credits on his CV.

Anthony Whitworth-Jones worked at Glyndebourne from 1981 to 1998, first as opera manager and administrator, and later as general director, ideally equipping to take up the challenge of stepping into the shoes of Garsington’s much-loved founder.

Like Ingrams, Anthony Whitworth-Jones has a passion for discovering little-known operas, and this year’s season features the UK premiere of Mirandolina by the Czech composer Bohuslav Martinù, who died 50 years ago.

Based on an 18th-century farce, La Locandiera (The Innkeeper) by Carlo Goldoni, the opera is a delightful comedy that Anthony is sure will be a crowd-pleaser.

“It’s a hugely entertaining piece, with music that is accessible and enjoyable, with individuality and some surprises. The production is going to be very, very colourful, in an almost cubist/Picasso way, but with very strong, vibrant colours.

“It’s about Mirandolina, who is irresistibly attractive and has many suitors. And the right suitor gets her in the end! I am completely confident that when people hear this they will absolutely love it.”

How did he discover this operatic rarity? “It’s part of my job to find operas which satisfy two criteria — they’re not well known, and they’re very good. There are lots of operas which are not well known for very good reasons. But there are actually many, many operas which people don’t know and which need to be discovered, and are worth performing. It’s part of the joy of the job, investigating the repertory and finding pieces like this one.”

Also featured in the season is Beethoven’s only opera, Fidelio, making its first appearance at Garsington, and Rossini’s La Cenerentola, making a welcome return to Garsington’s repertory after a 14-year absence.

This, of course, is Garsington Opera’s penultimate season at the manor that has been its home for 20 years. Rosalind Ingrams has decided, understandably, that she no longer wants her home subjected to two months of disruption every summer, and so the company needs to find a new home for the 2011 season.

For Garsington’s army of loyal supporters, it is the end of an era, but the good news is that its new home is likely to be in or near Oxfordshire.

“We’re still trying to get it sorted,” says Anthony, “but we’ve found some wonderful places, and we’ve got down to a shortlist — I can’t say more than that!”

Although sad about leaving Garsington, Anthony is excited and upbeat about the opera company’s future.

“It is a new beginning, and there’ll be continuity — the opera company will continue with its philosophy but in a different location.

“The character’s bound to change because it’s in a new place, but the ethos won’t change.

“The most important thing is that the property is right, that it has great charm and attractiveness, and the experience that people will have in the new location will be a wonderful one.”

lGarsington Opera’s 20th anniversary season runs from June 3 to July 5. Box office: 01865 361636. For more information, visit garsingtonopera.org