During the Wars of the Roses, Percy followed his father in siding with the Lancastrians against the Yorkists. The Earl himself died at what is generally considered to be the first battle of the wars, at St Alban's on 22 May 1455, and Poynings was elevated as third Earl of Northumberland, without having to pay relief to the Crown, because his father had died in the King's service. He in his turn "swore to uphold the Lancastrian dynasty". Although a reconciliation of the leading magnates of the realm was attempted in October 1458 in London, he arrived with such a large body of men (thought to be around 1,500) that the city denied him entry. The new earl and his brother Egremont were bound over £4,000 each to keep the peace.