Santander scam email
The strange thing was it came to a very old address which I very rarely use except for a few newsletters and it quoted my sister's name and a part of her postcode, both of which were correct.
I thought maybe a long time ago I had used that email address to register her but I don't remember doing so and she says she has never had an account with them.
The email seems to have come from someone using a Talk Talk account. My husband had a similar email, also via Talk Talk.