I live in an old house which is very long and has walls made of granite that a three feet thick. We have a basic BT Broadband package but cannot get any sophisticated broadband packages as we are out in the country with slow internet speed. Is there anything we can get, buy or do to improve the wifi reception in parts of the house which are distant from the router?
Wireless mesh systems are probably not going to be very effective with thick walls. The simplest solution is to probably use powerline adapters which provide a wifi hotspot via your mains wiring. Something like these https://shop.bt.com/products/bt-mini-wi-fi-home-hotspot-600-multi-kit-084289-BVFH.html
The master connects to your hub and the slaves can be plugged into any mains socket to provide a wifi hotspot.