Or might it be some sort of Lavatera?
For a long while we were pretty certain it was a Hollyhock, from one of the seeds Mrs Catspaw's father gave us last autumn.
But these aren't Hollyhock flowers. The best we can say for now is that it's clearly a member of the Mallow family (the Malvaceae).
Does anyone out there have a clearer idea as to what exactly it might be?