I think that this discussion may be at cross-purposes. GYH is a separation allowance which is based on mileage, not an actual number of miles that you drive (because you might fly or go by train). The mileage bit is just to allow some sort of measurement of separation. You can claim tax allowance on miles that you have actually travelled - on duty (certainly) or otehrwise (maybe - not sure), but that isn't GYH it's MMA (don't you just love JPA!?).