Chris, that link you gave ...
https://www.argos.co.uk/product/2473666
says that the Sony MDRRF811RK headphones are wireless with both Bluetooth and 3.5 mm jack being available.
Looking at them, it seems to me that they are both Bluetooth and RF, and they come with a 3.5 mm to RF adapter. If you use the adapter, you have up to 100m range (via RF, not Bluetooth) and the ability to connect to non-Bluetooth devices, and if you don't use the adapter you have a standard Bluetooth pair of headphones that you can use with a smartphone. Is that the case? It's odd because the manual makes no mention of Bluetooth, but the product description does.