Arum maculatum, aka 'cuckoo pint' and 'lords and ladies' amongst many other common names. It is difficult to control as weedkiller doesn't seem to work and if you dig them out, they have a small knobbly soil-coloured corm and these usually break-off and remain in the soil. Some folk like them and they're good for wildlife, although the red berries in summer are poisonous to us and every seed seems to be viable, so they spread easily.All you can do is dig them up from where they are unwelcome and try to get the corms out (that's also the only part which will have any roots on.) Because more will keep appearing in future years, just pull those up when seen and they will eventually give-up.
It's sold in the nursery I go to!!
There is a variegated form, which I grow.
The leaves die down after its flowered so it disappears during summer.
When you don't even know who's in the team
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.