"Stewart Robert Hinsley" wrote
Probably Malva moschata alba (white musk mallow) - there's a white
form of Malva alcea, but that's so rare I've never seen it. (The
easiest distinguishing characters for Malva alcea and Malva moschata
are not shown in the photographs.)

It looks like the white Musk Mallow to me too. I've got this growing in
my wild area where it seeds around in the grass, but have also added it
to the main garden border as it's such a lovely plant.

--
Sue