BabyStart Bed Rail
Fits to the side of the bed to stop a small child falling out.
Intended for 18 months to 5 years
For a single bed. Straps go under the mattress to secure it.
Mattress75-90 cm wide
You can see the sort of thing on Amazon
https://www.amazon.co.uk/Babystart-BabyStart-Bed-Rail-Natural/dp/B00MUZ6GNI
This one is a few years old so may not be exactly the same.
Good condition.
BabyStart Bed Rail (Old Swan L13)
This offer has been gifted to someone and is no longer available.