Found on the ceiling of my flat.
Place: London, UK
Date: 9th of August
Size I would say slightly more than inch and inch and half (3-4cm) wingspan
Suspect on the photo:
That looks very much like a brown color morph of the Box tree moth (Cydalima perspectalis), which has been seen in the UK since 2008. The size is about right (around 4.0-4.5 cm wingspan).
This species is an invasive pest outside of its native range (Asia).
By Nagy Sándor (NagySandor.EU) CC BY 3.0, Link
According to the Royal Horticultural Society this species has been invading the UK from the southeast with London a likely place to find them.