He gave a private recital with the pianist Ivor Newton on 9 March 1938 as "Yossef Hassid" at the home of Mr L.L. Gildesgame, 41 Clifton Hill, South Hampstead, where the guests included Sir Henry Wood. After giving a private recital at the home of Sir Philip Sassoon, Hassid made his public debut at a recital with Gerald Moore in the Wigmore Hall on 3 April 1940, billed as the "Polish Boy Violinist", playing works by Corelli ("La Follia" variations), Debussy, Schubert (Sonata in G), Bach (adagio and fugue from one of the unaccompanied sonatas), Paganini ("I palpiti") and others. The next day "The Times" wrote Hassid "showed imagination and musical insight" and that "his performance created a strong impression." Many years later Moore commented that Hassid was "the greatest instrumental genius I've ever partnered. I don't know how to explain his incandescence. He had technical perfection, marvellous intonation, glorious tone – but there was something above that which was quite incredible, a metaphysical quality. Sadly he had an unhappy love affair which literally drove him mad. But then maybe the unrest inside him made him play so fantastically." (Interview in "The Gramophone", April 1973.)