Struan Loy’s night had started promisingly. He’d had a date, his first in three years, and had planned it like an attempt at Everest, the base camps being wine bar, Italian restaurant and her place. Base one had proved a tremendous success, inasmuch as she had turned up; base two less impressive, as she’d left halfway through, and base three remained whereabouts unknown. Loy had returned home to an unmade bed and three hours’ sleep, interrupted by the arrival of Nick Duffy.
— Slow Horses (Mick Herron), Loc. 4254–7
Inasmuch as means ‘in the degree that’ (or ‘insofar as’), and it can also mean ‘since’ or ‘because,’ introducing a reason. In as much as.