He was disinherited by an act of parliament in 1550, although he had been reinstated as heir by the time of his uncle's death.Despite the fact that he had been reinstated as heir by his uncle, when the latter died in 1554 William West was unable to inherit the barony of De La Warr as a result of the Act of Parliament of 1550 which had deprived him of all honours.
Two years later he was involved in the Henry Dudley conspiracy, and on 30 June 1556 was arraigned at the Guildhall on charges of treason, to which he responded as 'William, Lord de la Warr', forcing the heralds to prove during the trial that he was not entitled to the barony and therefore not entitled to a trial by his peers in the House of Lords.
On 5 February 1570 he was knighted, and on the same day created Baron De La Warr, which was regarded as a new creation of the title.
By the modern rules of the House of Lords, his uncle's title fell into abeyance between the daughters of William West's second uncle, Sir Owen West, or their heirs; however, as Cokayne notes, such rules are at best modern approximations to actual medieval practice.
What seems clear is that some, but not all, writers treat the letters patent as clarifying the descent of the ancient title, rather than creating a new one, hence William is sometimes referred to as 10th baron.