Just idly browsing RightMove and I found this cottage in Cambridgeshire with exactly the bed I am looking for. It is picture 7. It looks to me like a bed that would fold from a single to a double. I really hope someone recognises the bed and can help. I've tried googling things like single to double bed and fold out double bed but not got anything so far.
yy it's a sofa bed. We have a very similar one in our spare room ( this ). To be able to fold the (shitty) mattress is split in two with a fabric 'hinge'. It can't be used as a single, is either a sofa or a double.