Pop-Up Opera is a remarkable company of limited means, but an abundance of ambition and musical gifts.

Formed by soprano Clementine Lovell in 2011 to make opera enjoyable and inviting to new audiences as well as seasoned fans, the company performs in pubs and theatres, plus a variety of unusual spaces – from a garlic farm to a candlelit cavern. As long as they can squeeze in a minimal set and a keyboard, the performance can begin.

Their current tour of Mozart's Così fan tutte gets off to a flying start in cosy new Mayfair bar The Whip, above the Running Horse pub. With its sofas, comfy chairs and racing prints all around the room, this feels very much like being in the sitting room of a great-uncle who loves horses. And opera, of course.

With a full house of around 25, the audience is up close and personal, and there's something quite stunning about being cheek by jowl with performers who are singing at full volume – the intimacy of the venue means we can see their tonsils quivering, and the youthful cast indulge in some very good-natured audience participation as they weave in and out of the seating.

The line-up varies from one performance to the next, but the company is largely made up of young professionals in the early stages of their opera careers. The full-toned voice of Eve Daniell, singing Fiordiligi, becomes richer and more confident as the performance progresses. Her younger sister Dorabella is sung by mezzo soprano Chloe Hinton, whose thrilling voice in "Smanie implacabili" has a purity and emotion that promises great things for the future.

Their lovers are played by baritone Oskar McCarthy as Guglielmo, suitably scathing in "Donne mie, la fate a tanti", and tenor Adam Torrence as Ferrando. And it's Torrence that the evening's ‘shiver down the spine' award goes to, for his beautifully moving and tender "Un'aura amorosa".

The costumes and setting are inspired by Downton Abbey, with cynical Don Alfonso (Alexander Learmonth) played as a wry butler who bangs the gong to let us know he's now in charge of proceedings, and determined to amuse himself at the expense of the young ladies of the house. Clementine Lovell's sparky, mischievous Despina – wearing a much shorter dress than the butler Carson would surely have allowed – helps him, unaware that she too is a victim of the men's tricks.

Pop-Up Opera are evidently operating on a shoestring, but their determination to produce great music is inspiring. Their shows aim to be accessible, fresh, surprising and fun, and they have succeeded all round with Così fan tutte.