During the reign of Henry II of England, Waleran's close ties to Louis VII of France caused him to fall out of grace.
As part of the family arrangement, Waleran also received a large estate in Dorset centred on the manor of Sturminster Marshall.
Late in 1122, Waleran was drawn into a conspiracy with Amaury III of Montfort, count of Évreux, in support of the claimant to Normandy, William Clito, son of Robert Curthose.
In October 1123, he lost his fortress of Pont Audemer on the Norman coast to a siege, despite calling in military help from his French relations and allies.
The returning column was intercepted by a force of knights and soldiers of Henry I's household between Bourgtheroulde and Boissy-le-Châtel, the royal commander being given variously as William de Tancarville or Odo Borleng.
The royal household troops decisively defeated Waleran in the Battle of Bourgthéroulde when he attempted a mounted charge at the head of his men, shooting their horses from under them.
At the court he was betrothed to the king's infant daughter, Matilda, and received the city and county of Worcester as her marriage portion.
In September he commanded the army of Norman magnates which repelled the invasion by Geoffrey of Anjou, husband of the Empress Matilda, daughter of Henry I.
He and his family began to monopolise favour and patronage at Stephen's court and they alienated the faction headed by Earl Robert of Gloucester, who in retaliation adopted the cause of his half-sister, the Empress.
Waleran fought on for several months, probably basing himself at Worcester, where he had to deal with the defection of his sheriff, William de Beauchamp.
At last late in the summer of 1141 Waleran gave up the struggle as news reached him that his Norman lands were being taken over by the invading Angevin army.
He consolidated his position as leader of the Norman nobility by a formal treaty with his cousin Robert du Neubourg, seneschal of Normandy.
[3] In Easter 1146, he was at Vézelay for the preaching of the Second Crusade and attended the great assembly of magnates at Paris from April to June 1147 to meet the pope and Louis VII.
[7] In 1149, Waleran started to lose favor with King Stephen, and was gradually excluded from power in Normandy, as his influence waned with the coming of age of Duke Henry and Geoffrey Plantagenet.
He made the fatal error of temporising with the Capetian court and assisting the campaigns of Louis VII, his overlord for Meulan.
Though his support gained Waleran the hugely profitable wardship of the great county of Vermandois during the minority of his young cousin Count Ralph II, it also led to his downfall.
In the second half of 1153, he was ambushed by his nephew and enemy Robert de Montfort, who held him captive in the castle of Orbec,[4] due to his link with Louis VII,[4] while his Norman and English estates were stripped from Waleran by Duke Henry's friends and officers.
Although Waleran was released, his power in Normandy was broken, and an attempt to reclaim Montfort-sur-Risle from his nephew was a humiliating failure.