Complex sentence: Realising that closing the base will impact upon the village's school (which only stays open because Eilidh pretends she cares for the children of the 300 base staff) he falsifies the report-and, much to his horror, is posted to the base permanently.
Split into simpler sentences: Realising that closing the base will impact upon the village's school, which only stays open because Eilidh pretends she cares for the children of the 300 base staff, he falsifies the report. But, much to his horror, he is posted to the base permanently.