Edward IV was much less respectful of sanctuary than his rival Henry VI. Though by no means seeking to dismantle sanctuary altogether, he was at times unprincipled in his disregard for the sacredness of the refuge and of his word. In this he followed the policy of his father, Richard duke of York, who did not hesitate to seize his rivals from sanctuary in the 1450s, including his own son-in-law.
Edward’s turn to breach sanctuary came first in early March 1470, in the months leading up to his temporary deposition. Richard Welles, Baron Welles, and his brother-in-law Sir Thomas Dymmok, were in league with those seeking to put Henry VI back on the throne. Polydore Vergil says that when Ed summoned Welles and Dymmok to answer for their actions, they took sanctuary at Westminster Abbey on 3 March, “meaning there to tarry until the king’s ire should be assuaged.” Edward sent messages promising them safety if they would come out of sanctuary.
“Upon the king’s promise” they came out of sanctuary. But when Lord Welles’s son, Sir Robert Welles, refused to stop leading his army against Ed, the king, “contrary to faith and promise given, and to the worst example that might be,” had Lord Welles and Dymmok beheaded.
In this case, the breach of the promise was seen (at least according to historian Polydore Vergil) as a potent example of faithlessness that lost Edward crucial support in the following months, leading to his deposition.
You’d think Edward IV might have learned from this, but apparently he didn’t; he committed even more outrageous breaches of faith and sanctuary when restored in 1471.