The footman moths have quite a distinctive rounded shape to the end of their wings and that helps when homing in on an identification. There are several footman species so it is good to have a starting point when trying to narrow down to the one you are looking for.
The buff footman (Eilema depressa) is typical of the range, with the rounded wings, and it is generally a buff colour so that is it, job done! I say generally buff coloured but caution is needed because it can vary from a pale grey through to a darker, almost slate grey colour. The variations are apparently more frequent in the larger females. The buff or straw colour is the most common however.
This is a nocturnal species flying in a single brood in July and August and sometimes into September if the conditions are favourable. It is very much a species of mature woodlands as the larvae feed on lichens and algae that occur on mature trees. That said, it is quite a common and widely distributed species so they do turn up in gardens.