He was seized at Great Harrowden (November, 1605) at the time of the Gunpowder Plot, but was eventually banished at the request of the Spanish ambassador (1606).
He had already begun to write on current controversies, and when James I of England desired a series of disputations in 1622, Percy, who was then in a prison in London, was required to defend the Catholic side.
These controversies were afterwards printed and discussed by Percy and John Floyd on the Catholic side, and by Laud, Francis White, John White, Daniel Featley, and Anthony Wotton on the Protestant.
[1] Percy was eventually released in 1625 and ordered to banishment in 1635; but he was allowed to remain in London until his death.
As a result of Percy's efforts, Mary, Countess of Buckingham and William Chillingworth became converts to the Catholic Church.