If it hasn't found its way out by tomorrow, I would go up in the loft and find where the ventilation space is that it got in through - it's probably under the eaves (? bit of roof that overhangs). Then I would place bird food type things (bread?) near this bit of the loft, to tempt the bird to consider that area more carefully.

Don't go too near the bird, and make sure you keep the loft hatch closed behind you, or it might try to get into the house to escape you. They're kind of tense about enclosed spaces, unsurprisingly for something that usually has miles of open sky around it.

The potential downside of this plan is the bird might think your loft with added breadcrumbs is a four-star bird hotel for the coming winter... your call :)

Regards,
Denny