At Urbino, the first important duty assigned to Castiglione was a diplomatic mission to London, as the representative of the Duke at the ceremony to nominate Guidubaldo into the Order of the Grater. Castiglione left Urbino in August 1506 and, passing via Lyon, arrived in England at the beginning of November. Right from the moment he landed in Dover on 20th October, he was the object of the solemn attentions of the dignitaries and ministers of the King. In London he met, Henry VII, in an atmosphere of reciprocal respect and friendship. Castiglione received from the King the gift of a gold necklace, a thoroughbred horse and pedigree dogs.
The mission was following a specific diplomatic strategy: Henry VII wanted, through Guidubaldo, nephew of the new Pope, to reach an agreement with Giulio II Della Rovere (to guarantee the legitimacy of his dominion), and the Duke Guidubaldo would receive in exchange a powerful ally for his small state.
Only one of the letters written by Baldassarre during his stay in London survives, and it was addressed to his mother: “Soche la M.V. desidera sapere de mì: però, quando posso, non manco de scrivergli.Cussì li facio intendere come el primo de novembre io gionsi qui in Londra,ch’è el capo de Inghilterra, sano e salvo, per Dio gratia, acompagnatohonoratissimamente. E qui restato dui giorni, chiamato, andai a la Sacra M.tàdel Re, che me ha fatto grandissimo honore, e careze, et ogni zorno fa più: sìche io spero satisfar bene a la Ex.tia del S.r mio, et anchor a Sua M.tà, etornarmene sano in Italia” (I know that my dear mother wishes to hear from me: so,when I can, I do not forget to write to her. Thus I let her know that on 1stNovember I arrived in England, safe and sound, by the grace of God, inhonourable company. And here after two days I was called by His Royal Highnessthe King, who honoured me and gave me gifts, and every day does more: so I hopeto satisfy my Illustrious Master, and also His Majesty, and to return safely toItaly) (B. Castiglione, Lelettere, edited byG. La Rocca, I, Milan 1978, 100).
On returning to Italy in 1507, after a fleeting visit to his mother, he went to Bologna to Pope Giulio II and Duke Guidubaldo; he then returned to Urbino in the following March, welcomed by the felicitations of the court and friends, to whom he was able to give an exact account of all that had happened.