LONDON  If the Ukulele Orchestra of Great Britain exists partly to subvert expectations, then the first expectation it subverts is that it is going to be very, very bad.

“Relief is one of the major emotions of our audience,” declared Dave Suich, an orchestra member.

But the happy surprise of encountering something completely different from the Tiny Tim-style hamming or banjo-plucking embarrassment of your imagination doesn’t wholly explain the deep love the orchestra inspires, not just in Britain, but also in Europe and as far away as New Zealand and Japan. Previously the private passion of a large but sub rosa group of devotees, the orchestra hit mainstream popularity last month when it performed to a sold-out crowd at the BBC Proms music festival at the Royal Albert Hall here.

“They have grown into a much-loved institution,” The Observer of London wrote. In The Financial Times Laura Battle praised the orchestra members’ “consummate skill” and said that the “sophisticated sound they make  both percussive and melodic  is at once hilarious and heartfelt.” The Evening Standard said, “The country would plainly be a happier place if more of us played the ukulele.”

Part of the appeal is that the group  eight of them, all singing and playing the ukulele  extracts more than seems humanly possible from so small and so modest an instrument, with its four little strings. Part of it is the members’ deadpan sense of humor, in which they laugh at themselves as much as at the music.