Restormel has seen action only once during its long history, when a Parliamentary garrison occupied the crumbling ruins and made some basic repairs during the Civil War. It was invested by an opposing force loyal to Charles I, led by Sir Richard Grenville, a local member of the gentry who had been the member of Parliament for Fowey before the war. Grenville stormed the castle on 21 August 1644, whilst manoeuvring to encircle Parliamentary forces. It is not clear whether it was subsequently slighted but in an Parliamentary survey of 1649, it was recorded to be utterly ruined with only the outer walls still standing, and was deemed to be too badly ruined to be repaired and too worthless for there to be any value in demolishing it.