Musical celebrities who heard him play at Flesch's house and were astonished at his ability included Joseph Szigeti, Jacques Thibaud, David Oistrakh and Fritz Kreisler.
Three weeks later, on the evening of 25 April, he made his orchestral debut at the Queen's Hall in a Polish Relief Fund concert (broadcast on the BBC Home Service) playing the Tchaikovsky Violin Concerto with the LPO under Grzegorz Fitelberg (during which he suffered a memory lapse).
The next day The Times reported that Hassid "showed some signs of nervousness at the outset", but "the beauty of his tone was striking and the brilliance of the finale" earned him generous applause.
On 9 June 1940 he was due to appear with Eileen Joyce as a supporting artist for Richard Tauber in a concert at the Colston Hall, Bristol, but was replaced in the event by the cellist Eleanor Warren.
He gave a few recital broadcasts on the BBC and played the Beethoven Violin Concerto during an afternoon concert in the Queen's Hall with Sir Adrian Boult conducting the London Philharmonic Orchestra on 5 January 1941.
The solo performance was scarcely more than that of a clever student who has worked hard to memorize the concerto but is still liable to be thrown off his stroke, even to the point of forgetting his notes occasionally.
Hassid's agent, the impresario Harold Holt, wrote to the superintendent of St Andrew's: "He is nothing short of a violinistic genius and of such exceptional quality that we want to make the greatest effort possible to cure him.
"[4] His condition improved for a time, and he left the hospital on 2 May 1942, but on 9 December that year, he was certified insane and admitted to Moorcroft House, a private asylum in Hillingdon, Middlesex, three days later, for further treatment.
17) with accompanist Ivor Newton at the Abbey Road Studios on 9 January 1939 when Hassid had just turned 15; and then Walter Legge produced a further eight recordings on 12 and 28 June and 29 November 1940, this time accompanied by Gerald Moore.
Even so, his performances of Joseph Achron's Hebrew Melody, Sarasate's Zapateado and Kreisler's Caprice viennois in particular are superb and show virtuosity of the highest order in expressive phrasing.
To quote from Bryan Crimp's note with the Testament CD: "The moment Hassid puts bow to string he beguiles the ear via a captivating and uniquely individual sound ... a peerless technique and an arresting and frequently original interpretative approach.