With an army reinforced by 15,000 Londoners, he marched in May to the relief of the Cinque Ports which were now threatened by the king.

Even on the march he was forsaken by many of the nobles who followed him.

Halting at Fletching in Sussex, a few miles from Lewes, where the royal army was encamped, Earl Simon with the young Earl of Gloucester offered the king compensation for all damage if he would observe the Provisions.

Henry's answer was one of defiance, and though numbers were against him, the Earl resolved on battle.

His skill as a soldier reversed the advantages of the ground; marching at dawn on the 14th of May he seized the heights eastward of the town, and moved down these slopes to an attack.