Caceres is described as a chauvinist Jew, boastful of his Jewish descent. He joined Antonio Fernandez Carvajal in the acquisition of the Bet Cholim cemetery in London, and was one of the petitioners who signed the document presented to Oliver Cromwell by Manasseh ben Israel in March 1656. Queen Christina of Sweden is known to have interceded with Cromwell on his behalf for certain commercial privileges in Barbados. At a later date the king of Denmark gave Caceres's brother a letter of recommendation to Charles II of England, which was instrumental in procuring for the Jews in the West Indies an extension of commercial facilities. Simon was one of Cromwell's intelligencers; and there are at least two documents among the Thurloe papers which show that his experience was utilized by the lord protector. One is called "A Note of What Things Are Wanting in Jamaica". It is a memorandum containing minute advice with regard to fortifications and implements. From a passage in "Cromwell's Letters and Speeches", ed. Carlyle (iii. 131), it would seem that Caceres's recommendations were followed, for the needed supplies were forwarded.