Despite the defeat of Admiral John Byng’s relief force at the Battle of Minorca, the British garrison held on until crumbling walls and the exhaustion of the defenders caused Blakeney to capitulate with the honours of war. Under the terms of the treaty Bastide and the other survivors of the garrison, were transported back to England. On 14 May 1757 all engineers on the establishment were given military commissions and Bastide duly became a lieutenant-colonel.