Ash glaze, cup incised decoration

Hi, please help with ID of this cup - this is my first post and there may be a few more as I have hundreds of unknown pieces. Thank you! I live in Devon so there will be a few Devon makers among them.
Cup is 10.5 cm tall, no mark. Looks like ash glaze on upper half, an unglazed brown finishing middle, with sgraffito decoration. Fairly coarse grey body. Well thrown.

So this was my first post over 2 years ago.
Thank you everyone for your help over that time. I’ve learned lots.
I’ve still got quite a few unidentified pieces left so I thought I’d just put this out again in case someone recognised it.

The decoration reminds one a bit of Marianne De Trey.
You must have had a tremendous number of pots Ben. Were they all your mother's? It would be fascinating to know how the collection was built up.

Mums and lots of mine over years. I think mums first piece of pottery she bought was a tile from the Leach pottery in about 1945! Shame she didn’t buy more from there.
Shame there’s no mark on this cup as it’s well made.