Plus the 600ft. elevation, plus the diversion fuel to an area with a marked difference in meteorological conditions, plus the holding fuel, plus 10%.
Point was, if the weather is that bad I'd rather fly routine IFR to a lit IFR runway with IFR reserves (and continue operating down to a met vis of 500m), than 'VFR' to Penzance in marginal weather with a minimum met vis of 1500m. The IFR fuel reserves (if workable) ADD safety over flying marginal VFR, and I'd rather plan a straightforward IFR routing than have to convert to IFR when VMC is lost and end up diverting to an IFR airport anyway, perhaps without IFR reserves?