This page contain information about shelters other than Anderson, Morrison or deep shelters.
Here are two photos of a concrete shelter in Langley, Buckinghamshire. The owner, Kavitha Anand, would be very interested to hear from anyone who can shed light on its history - as would I ! (Email to firstname.lastname@example.org ).
And here is a strange Anderson-shaped concrete shelter in Alcester Street, Stoke, Plymouth:-