1 have a 5c master socket which runs my phone and bt hub in the house I have a barn next door (20meters) and would like to a cable to it to run another bt hub and phone (same number ) can any body give me some advise on how to do this
You can't. You can have a phone on the extension but you you can't have 2 hubs. To extend the phone run a cable from terminals 2&5 in the removable front faceplate of the master to terminals 2&5 on an extension socket in the barn. If you want internet connection in the barn you will need to connect the 2 hubs via Ethernet and configure the barn hub as a pseudo wireless access point. If the barn is on the same consumer unit as the house, it might be simpler to just use powerline adaptors such as these. https://shop.bt.com/products/bt-mini-wi-fi-home-hotspot-600-kit-084288-BVFF.html
You could either run an Ethernet cable from the Hub to the barn and connect a wireless access point to it or if the barn is on the same electrical circuit going through the same consumer unit as the house you could use Powerline adaptors to get your broadband signal to the barn.
See link for BT ones but you can use any manufacturers.
EDIT: Posts crossed with liquorice's post.
You cannot connect a hub or any router to the same phone line as existing hub. Only 1 router to a phone line
No, you can't have 2 DSL routers of any description on one line.
You can connect a wireless access point by Ethernet cable to your hub or convert a spare hub/router as a pseudo access point as I said before. To do this you need to give the second hub an IP address outside of the DHCP range of the main hub, turn off DHCP on the second hub/router and connect the 2 devices LAN port to LAN port via a CAT5E Ethernet cable.