I assume that you are referring to the death of Sir Thomas More as depicted in the play, A Man for all Seasons, by Robert Bolt, which has also been made into a movie. Although this play is based on the real life of Thomas More, Chancellor of England, the playright has used "poetic license" to infuse his own political thoughts into the action, so not everything that occurs in the play is necessarily historically accurate. That, said, back to your question.

In the play, Sir Thomas More, an important government official and back in those days, affiliated with the Church of England, refused to sanction King Henry VIII's divorce from Catherine of Aragon so that he could marry his mistress, Anne Boleyn. More believed that this would be a sin because the church did not sanction divorce. More's opponents included King Henry, Cromwell, Wolsey, Cranmer, Chapuys, and Norfolk. In the play, they are depicted as being either corrupt, evil, and/or power-hungry, more concerned with pandering to the king and thus keeping their earthly power. More contends he answers to a higher power.

In the play, the Spanish get involved because Catherine is a Spanish princess. They plot to attack the king, telling More about it hoping he will agree with them. More informs Norfolk of the plot, however, showing loyalty to the King. More also refuses to speak against the king, and in the play, it appears that Cromwell prosecutes him out of personal spite. Cromwell is the major antagonist in the play. Eventually, More is executed after a convoluted series of legal maneuvers for breaking the law.

You will no doubt receive several opinions as to who is responsible for More's death, but my opinion is that it is King Henry VIII. If he had not been so intent on having a son, no matter what it took, the entire affair would not have even taken place. There would have been no attempted divorce, there would have been no break with the church of England, and there would have been no subject matter for the play in the first place. Henry was king and the buck stops there. The way the monarchy was set up in those days, the king could have done pretty much what he wanted, including stay the execution.

Thomas More was eventually made a saint in the Catholic Church.