Two possibilities:
Beaufighter X7548 of 604 Squadron, which crashed between Pewsey and Marlborough on 26 July 1941. Flight Lieutenant H Speke and Sergeant GL Dawson were killed
or
Tutor K3400 of Central Flying School, Upavon, which crashed 'near Pewsey' on 2 January 1942. Sergeant JE Chodzicki (Polish) was killed.
EDIT:
Speke was killed on 26th July 1941 on a routine night flying test in Beaufighter X7548 NG*S. The aircraft struck Oare Hill, Pewsey, Wiltshire at high speed, the cause was never discovered. So probably not this one, as Oare is in the wrong direction, away from the white horse and other side of town.
Chodzicki's first name was Jerzy; after performing a series of manoeuvres, he tried to forced-land in near Pewsey and crashed in doing so.