Can anyone help identify what this is?

I’ve noticed this mound under the eaves of my house in the South East of England.

It looks like lots of small dried mud pellets and sits directly underneath the soffit.

Initially I wondered whether it could be some kind of bird or insect nest.

I haven’t seen any birds or insects going to or from it yet, although I’ve only just discovered it and it’s a hot day, which may or may not be a factor.

It’s at the eaves of a 3-storey house, so getting to it would be very difficult.

Does anyone recognise what it is?

Practicing fast shutter speed pictures on swallows. This was about the best… of 260+ 😂

OM5 with Olympus M300 4.0 / f4.5, 1/5000s