Complex sentence: They worked together to produce a one-minute test sequence of colourised shots from the episode which eventually led to the Doctor Who Restoration Team approaching Humphryes in 2011 to officially engage him to recolourise the serial.
Split into simpler sentences: They worked together to produce a one-minute long test colourisation of various shots from the episode. It was due to this experimental work that Humphryes was approached by the Doctor Who Restoration Team in 2011 and officially engaged to recolourise the serial.