These two species can be found flying at the same time of year. In Bedfordshire The Tissue is the the rarer.
Separation is best done by looking at the markings on the underside of both fore and hind-wings. This is easily checked by using a clear plastic box or jar.
Scarce Tissue has two obvious dark marks on the underside of the leading edge (costa) of the forewing near the head of the moth which are lacking in The Tissue. The dark central mark on the wings are more prominent and there is a prominent black wavy sub-terminal line on the underside of the hind-wing. The underside of a Scarce Tissue is illustrated below