This pillbox is as far as I know unique in Suffolk, although not that rare as an airfield pillbox in the rest of the country. The following is from M Osborne's Pillboxes Of Britain and Ireland:
"This structure is described on official Air Ministry plans as the Mushroom, the Oakington and the Fairlop, and is associated with drawings numbers TG14, 9882/41 and T/5291; it consists of an open, circular pit.......and domed concrete roof, cantilevered off a central pillar, either cruciform or butterfly, and forming AR walls; a tubular rail, holding two movable , clamped mg mountings, is fixed below the parapet, giving a 360 degree field of fire; it was widely used for airfield defence...."
Above: The "Mushroom" Pillbox, Honington.
Above: Views from the interior of the pillbox. Note the cruciform central pillar.