He was accustomed to the world's finest concert halls, but he never forgot the profound impact that these wartime concerts had on their listeners.
Three decades later, Menuhin created a charity called Live Music Now with two primary goals. First, he wanted to find a way for high-quality music making to reach isolated members of the community. "Music," he wrote, "amongst all the great arts, is the language which penetrates most deeply into the human spirit, reaching people through every barrier, disability, language and circumstance. This is why it has been my dream to bring music back into the lives of those people whose lives are especially prone to stress and suffering ... so that it might comfort, heal and bring delight."
Menuhin's other ambition was symbiotic. Always the pedagogue, he wanted the charity to work as a springboard for young artists - to develop their early careers, broaden their communication skills and ensure that their language speaks to everyone.
Live Music Now began in London, but its reach spread fast and far and branches soon sprang up around the UK. The first outside of London was established in Yorkshire in 1980; a Scottish chapter followed in 1984, 30 years ago this year. Chances are that you've heard a Live Music Now Scotland (LMNS) gig, maybe without even realising it.
It could have been a brass quintet under a gazebo on the High Street in Crail, or a string quartet on the concourse of Glasgow Central Station; a song recital in the National Museum of Scotland or a fiddle duo in a hospital or a care home. For 30 years, Live Music Now Scotland (LMNS) has been performing live concerts to audiences who would not otherwise have the chance to hear them.
Carol Main has been at the helm since the start. She originally took on the work for an afternoon a week; now she presides over a Live Music Now umbrella that extends around the world. There are branches across Europe, projects in Indian and Abu Dhabi and a sister charity called Musica Para Todos in Chile.
"There is a need for what we do everywhere," she says. "And frankly a need for more than what we're able to deliver."
Inevitably money is the limiting factor, but through fundraising and working with partner organisations like the National Gallery and the National Museum of Scotland, LMNS has been able to present around 600 concerts annually in recent years.
It's the audiences, says Main, who keep her cheerful through the mountains of funding proposals. She tells me about a woman whom she met after one museum concert: this woman had a severely disabled son who could not usually enjoy live music without fear of letting out an uncomfortable noise or distracting gesture. This had been the first time her whole family had been able to attend a concert together.
The young musicians who perform the concerts tend to be in their twenties, recently out of music college and forging their way as freelance professionals. What does Main look for in applicants? "Musicians who want to communicate," she replies. "Who use eye contact with each other and with the audience; who clearly enjoy what they do; who are secure enough musically that they'll be able to focus on communication are not just wrapped up their own world."
After applying, musicians attend several concerts and extensive discussions with previous LMNS artists and the charity's directors. "They really need to have a full understanding of what's involved before they sign up," says Main. "This kind of outreach work is by no means for everyone."
Once accepted onto the scheme they receive wide-ranging support for several years. LMNS provides mentors and training sessions - courses on everything from how to file a tax return to how to deal with press and PR, from image consultants to how to work with people with dementia. They're given photoshoots and professional marketing material. "These are elements of the industry that can be mystifying and daunting for new freelancers," says Main.
"It's crucial that young professionals develop flexible ways of working. Great as it is to see musicians securing full-time orchestral contracts, those kind of opportunities are few and far between and most graduates from conservatoires will have to be a lot more versatile."
The list of LMNS alumni speaks for itself. The soprano Lisa Milne launched her career with the charity - Main describes a performance Milne gave at St Columba's Hospice as "a highlight of the past 30 years".
Dundonian accordion player James Crabb "always stunned folk in care homes by turning up with an accordion and playing classical repertoire rather than the jigs and reels they expected".
There is also pianist Malcolm Martineau; singer and radio presenter Jamie MacDougall; cellist Alasdair Tait; BBC Scottish Symphony Orchestra principal flautist Rosemary Eliot; singer and broadcaster Mary Ann Kennedy; concertina player and Hands up for Trad founder Simon Thoumire.
"Many of our former members are associated not just with excellent musicianship," says Main, "but with ongoing outreach, education and communication."
In recent years LMNS has also begun to commission new music, and the 30th anniversary has been marked by a substantial new string quartet by Alasdair Nicolson. Called The Keeper of Sheep, it's an evocative, poetic, challenging work full of shifting textures and vivid images. I heard the premiere last month in Orkney, where the Astrid Quartet had their work cut out just to hang together; the quartet has another stab at the score next week at the Music at Paxton festival near Berwick upon Tweed.
These concerts in Orkney and Paxton represent the work that LMNS does across the length of the country. A series of free concerts at the National Museum of Scotland in August - every day of the Fringe, no less - represents the breadth of their activities. It's a fitting tribute to a tremendous 30-year legacy, and to the strength of Menuhin's vision.
Music at Paxton is July 18-27. For more information on Live Music Now Scotland visit www.livemusicnow.org.uk