RJ11 Male to Male cable with a coupler supplied (the picture shows the coupler attached). Can be used with the coupler to extend an existing cable or without the coupler to just replace an existing cable.
eBay
1pc UK power cord universal socket compatible with multiple plugs 1/1.8/5/10/15/20m 3250W home office extension cord sockets
Aliexpress UK
The cabledUp® BT Telephone Extension Cable is a versatile and reliable option for extending the reach of your home phone. Available in lengths ranging from 2m to 20m, this fully wired 4 pin male to female lead is compatible with most universal phone models. The flat cable design ensures easy installation and a clean look, while the white colour adds a sleek touch to your home decor. With a 1:1 connection split/duplication, this cable provides a direct and efficient connection for your telephone. Ideal for expanding your home phone system, this extension cable from cabledUp® is a practical and convenient accessory.
eBay
DC 12V Power Adapter Extension Cable 3M/5M/10M/15M/20M/30M DC Male Female Connector Power Extend Cord For Security CCTV Camera
Aliexpress UK
The Link-it 20 metre phone extension lead is a versatile and practical accessory for your home phone. With a flat cable design and a length of 20m, it provides ample reach for connecting your phone to a distant power source. The white colour and universal compatibility make it a sleek and convenient option for extending your phone's reach in any room.
eBay
16-30AWG 5/10/20M Red Black Electrical Wire LED Strip Cable 2 Core Tinned Copper Extension Power Cord For Lighting Audio
Aliexpress UK
*Black Internal Cable Don't think it's External Grade, Very Rare as Most cable is white Cable The product is a 11.6m of Black BT telephone cable wire with 2 pairs of 4 core extension. Made of solid copper, this cable is ideal for connecting home phones and accessories. Manufactured in the United Kingdom, this high-quality cable ensures reliable communication and transmission of signals. Perfect for extending the reach of your telephone lines, this cable is a convenient and essential addition to your communication setup.
eBay
1.5/3/5/10/20M 3.5mm Stereo Male to Male Jack Male to Female Audio Aux Extension Cable Cord for Computer Laptop MP3/MP4 H10
Aliexpress UK
FOR BROADBAND OR PHONE – A professional grade kit that has been simplified by a Telephone Engineer in order to allow anyone with the need to run their own extension at a fraction of their service providers cost BEWARE OF FACTORY KITS - There is currently a surplus of imitation copper cables on the UK market.
eBay
Black 1.0M 2.0M 3.0M PVC Copper IEC320 C13 C14 C15 C19 C20 extension power cord 10A / 16A charging cable
Aliexpress UK
Simply connect your device into the the female socket of this cable and connect the plug into your existing wall socket.
eBay
5m/10m/20m 2Pin 12V Electrical Wire Tinned Copper Cable 2 Cores Insulated PVC Extension LED Strip Cable 20 22 18 AWG Gauge Wire
Aliexpress UK
TELEPHONE AND SUPERFAST BROADBAND - These cables are perfect for extending both Telephone and Broadband signals around the home. They are compatible with BT Infinity, Sky, EE, Plusnet, Virgin Telephone, TalkTalk and many other Internet Service Providers BEWARE OF CHEAP IMPORTED VERSIONS - There is currently a surplus of imitation copper cables on the UK market. Many copies of BT CW1308 cables claim to be manufactured to BT spec but instead use either Copper Clad Steel (CCS) or Copper Clad Aluminium (CCA) AVOID SLOW BROADBAND + A QUIET PHONE - Using the incorrect cable can have a dramatic effect on Router speeds and even the volume on your Telephone line.
eBay
5M 10M 20M 2Pin 22AWG Extension Wire Cable Use for 12V 24V 2835 5050 Single Color LED Strip Light Red Black Electric Cord Line
Aliexpress UK
Installation is simple and straightforward with plug-and-play functionality. There's no need for complicated tools or technical expertise—simply plug in and extend your phone line to any room or workspace.
eBay
1.5/3/5/10/15M/20M 3.5mm Male to Male Jack Audio Stereo Aux Extension Cable Cord for TV Computer Laptop MP3/MP4 E3
Aliexpress UK