It is a Winter Moth unsurprisingly, a fascinating species whose 'blood' is akin to anti-freeze which allows it to thrive at this inhospitable time of the year. This one is a particularly impressive example of the survival of the fittest, having found its way into our cosy home.
Or is it? Given that it has the means to survive outside, perhaps it is risking the weakening of its powers, and those of its descendants, by taking this superficially cunning step. You can read a bit more about the antifreeze side of things in this post from January two years ago.