@Boucks 

Hey and Welcome!

Another UK based user im guessing?  Also a BT customer here so might be able to help you. 

Ok so you say you are using TP Extenders, would you give us the model of these?  It should be on the back near the serial, that way I know what we are working with.

In relation to the BT Hub, sadly you cannot seamlessly roam from the Hub to anything other than the BT discs (explain below).   For seamless roaming to work the hardware has to support it, and 99% of the time needs to be from the same vendor.   Depending on the extenders you have, you could go for a TP Link One Mesh, if thats possible.. will know more with the model numbers.

Failing that a mesh via TP link is not an option, then BT Discs or Deco is the next answer for you.   BT discs are a bit MEH if honest, but cheap as BT provide them for £5 a month or something like that..  Deco is around £60 to £90 depending on how many you need, but that is a one off cost.

Mesh systems like the Discs and Deco are basically the best way to get a single WiFi around the house with roaming.   There is one base node (BT hub or Main Deco) and the other nodes dotted around your house act like repeaters bouncing the signal around as one network.    Extenders cant do this as they generally are stand alone devices and dont talk to eachother, therefore they cant "seamlessly roam" you as you move.  They also appear as 4 or however many WiFi connections which is annoying. 

Stick me through the details of the extenders you have and we can see what options are for you.

Philbert