Posted: 08/06/2013 at 08:12
This sounds to me to not be Arum lilies - Zantedeschia but probably Arum maculatum - commonly known as Lords and Ladies or cuckoo pint.(have a look at google images)The flower shape is similar to arum lilies but they are completely different plants. They are a British wild flower which can become a troublesome weed. Lords and ladies are prolific spreaders and can take over places. I would think glysophate is the best way to get rid of them. Let the leaves grow, remove by hand any flower spikes(to prevent seeding) and zap the leaves on a still day ensuring the spray does not hit surrounding plants - you may have to bruise the leaves first as they have a waxy coating which will prevent the chemical being absorbed!.