Thus William was a nephew of the Empress Maud and a first cousin once removed of King Stephen, the principal combatants of the English Anarchy period.

In October 1141, William looked after the Baronial estates, when his father fell into the hands of partisans at Winchester.

In 1154, he made an alliance with Roger de Clare, 3rd Earl of Hertford, by which they agreed to aid each other against all men except Henry II of England.

Because his only son and heir, Robert, died in 1166, Earl William made John, the younger son of King Henry II, heir to his earldom, in conformity with the King's promise that John should marry one of the Earl's daughters, if the Church would allow it, they being related in the third degree.

But, during the King's struggles with his sons, when he imprisoned a number of magnates of whose loyalty he was doubtful, Earl William was among them.