Newark’s first Anson largely went up in smoke in 1971, only the wings & engines were saved.

Newark’s first Anson was the original Ekco testbed from Southend G-ALIH. The radar nose was removed at Southend and swapped with the original nose from its successor G-AGPG before the transfer to Newark where some kind soul torched it one night.
Not exactly a major fire but the paint store and workers hut at the Southend Museum burnt to the ground when I was a volunteer there. I arrived one day to find a scorched wooden floor where the building had stood a couple of days before. The fire damaged Dragonfly WG725 which had been stored in pieces beside the hut ever since arrival from Blackbushe. I think the Dragonfly eventually landed up as scrap as in those days the fire damage meant it was regarded as past restoration. Fortunately the fire didn’t reach our spare Sea Fury WJ244 which was lying dismantled next to the Dragonfly. The cause was traced to it being a very hot day and the paint store had poor ventilation. It was believed that the fumes from the paint and thinners eventually ignited causing the fire.
The Gemini at Southend was dismantled after an attack by vandals and the deterioration of Anson G-AGPG also started after it the fuselage fabric was slashed by vandals. I know that the cockpit of Beverley XB261 was also damaged. All 3 of these incidents actually took place during museum opening hours but the manager at the time had cut back on staff so the scum were never caught.