Classic British Horror Movie.?

What's the name of this movie from the 50's or 60's. They are on a small island and a scientist was working with radiation and created these creatures that look like human brains that slide along the ground. They are about 4 feet in diameter and have a trunk thing that sticks up like a neck. They split every couple of hours and so the number of them doubles and they are eating all the cattle on the island and people too and the islanders have to hole up in the local school until they figure out how to get rid of them. Thanks.