Flinter, an Irishman by birth, entered the British Army in 1811 as an ensign in the 7th West India regiment of foot, and was advanced to the rank of lieutenant on 22 July 1813.
He was treated with great distinction by the Spanish Captain-General Juan Manuel Cajigal, and he obtained employment as interpreter between the Spaniards, English and Americans.
Though he remained on the British half-pay list until 1832, he had for some years before that date held the position of a staff officer in the Spanish service, after which time he wrote a lengthy account about the colonies of Spain (Puerto Rico and Cuba) and his opinions about slave labour.
[1] On the outbreak of the First Carlist War in 1833 he declared for Isabella, and in 1834-1835 he served under Mina and Valdez in their unsuccessful operations against Zumalacárregui in the Basque provinces.
In 1836, while engaged in organising the militia in Estremadura, he was surprised by some of the troops of Gomez and Cabrera, taken prisoner, and thrown into a loathsome dungeon, from which by the connivance of his gaoler he contrived to escape, and made his way to Madrid.