If you still have the have the Talktalk router you can do the following...
Connnect the Talktalk router directly to your pc and switch off DHCP using the Talktalk admin page. Keep the SSID as Talktalk12345 or whatever it was. Set the wifi channel as something away from the SH wifi channel (or use auto). Disconnect the Talktalk router from your pc.
Keep the SH in router mode.
Connect the talktalk router to the SH via ethernet (use LAN ports on each). You'll then have VM wifi and TT wifi. Assuming the SH is located where the TT router was previously installed you should have good wifi coverage from the TT router.
You can clean up SSIDs etc at a later point in time if you wish.
A new decent router or mesh wifi will be better but the above is free of charge.