The Commonwealth had grown suspicious of monarchist plots, and fearful that the large group travelling with George Fox aimed to overthrow the government – by this time, his meetings were regularly attracting crowds of thousands. In 1653 Fox was arrested and taken to London for a meeting with the Lord Protector, Oliver Cromwell. After affirming that he had no intention of taking up arms, Fox was able to speak with Cromwell for some time about the differences between Friends and members of the traditional denominations, and advised him to listen to God's voice and obey it.
The following passage by Fox tells something of the understanding between them.
"As I was turning, he caught me by the hand, and with tears in his eyes said, “Come again to my house; for if thou and I were but an hour of a day together, we should be nearer one to the other”; adding that he wished me no more ill than he did to his own soul. I told him if he did he wronged his own soul; and admonished him to hearken to God’s voice, that he might stand in his counsel, and obey it; and if he did so, that would keep him from hardness of heart; but if he did not hear God’s voice, his heart would be hardened. He said it was true."
More at http://en.wikipedia.org/wiki/George_Fox#Encounters_with_Oliver_Cromwell