A 70-year-old man presents to the ER with an acute disturbance of vision and balance. He explains that whilst sitting in his chair at home earlier in the evening the room suddenly began spinning. When he tried to get up, he felt dizzy and kept bumping into furniture. On examination, he has nystagmus and a left homonymous hemianopia. He is noted to be hypeensive (BP 170/80) but all other vital signs are within the normal range. An MRI head reveals an acute ischaemic infarct. According to Bamford classification, what type of stroke has this person suffered?