If an RJ11 won't help what are you trying to do? The connection between master socket and hub is RJ11.
Amazon is an online store so there won't be one near you. Argos, Tesco, Asda, PC World Curries and Maplan will all sell them but expect to pay significantly more. You may wish to try Ebay.
if you are going to run extension cable for any distance then I would just buy a new shielded rj11 cable like this it may look like an ethernet cable but it is a rj11 cable - i use one at present
Thank you for that but no it's definitely not the cable I need so glad I didn't have a wasted trip to Argos. I'm after one of the black ones with the yellow plugs.
The colour of the cable and the colour of the plugs are irrelevant, they can come in many colours but have the same core to the cable and connectors. It is the type of plug that you need to specify. If you are not sure you should say what you are wanting to connect the cable from and to and somebody might be able to tell you what cable and connectors you need.
'The black ones with the yellow plugs' are normally Ethernet cables which connect hub to device not hub to openreach wall socket
it would be a help as suggested you are more specific what you are trying to achieve