It's Kerria Japonica or Jews Mallow. It is particularly good in Norfolk this year, yours looks well. Don't forget to cut back flowering shoots (after flowering) to strong new growth. Over the years the plant does tend to 'wander' a bit, so try to keep it in one place (if you need to)

Thanks for that. Found it now but with only a black & white illustration so I didn't pick it up before.

If you google Kerria japonica pleniflora you will get lots of colour photos of your plant.