The TP Link Td-W9970 router is about £40 at Argos and £33 at Amazon. The wifi can be permanently turned off.
Be aware that placing the hub in a bag could cause over heating issues.
licquorice - I was more than happy with my old hub but because it was actually impossible to switch off the shared WiFi, I requested to change to the latest version because it had the facility to do so, and for no other reason. So yeah, it may well be part and parcel of the default setup, which I was happy to agree to........ however.......
There is no difference in whichever hub you use in respect of turning off wifi. The turn off needs to be done at the network level as well as your hub in order to prevent you accessing the signal whilst out and about but not transmitting at home, hence it can't be turned off locally on the hub.
To avoid confusion when using the generic term "wifi" can we refer to the "normal" signal emit by the hub as the "wireless" signal and BTWifi with Fon or BTWifi X by their names.
For the sake of a few quid I suggest you buy the router mentioned.
ALL wifi on that device can be turned off permanently. Even if you opt out of BT wifi with Fon, it is apparent from other posters that it can be re-enabled with firmware updates to your hub and need opting out again.