You can buy the correct cable from your local B&Q. Called something like satellite cable. You need a small spanner to tighten the connections at both ends.
Not sure what lengths you can buy, but I think mine was about 4m.
You can get the bits to make your own up to about 25m for around £10, just get a roll of cable (specifically for satellite) and a packet of F connectors (£1 for 2) from B&Q. This way you can make it as long as you want and have spare to allow you to hide the cable if you need