How do I get the extension kit?

[#1]

Got FTTC installed ten days ago and it is working a treat, 37Mb/s so much nicer and faster than 0.7Mb/s I was getting on ADSL.
The engineer installed the Openreach modem by the front door, not quite next to the power socket but close enough.
Anyhow my original plans to shove it all in the cupboard by the front door haven't quite worked out.
So what I want to do is run a long extension cable from the master plate to the Openreach modem.
Is this possible, I have looked over the BT site and it isn't clear if the extension kit is a cable between modem and hub or master socket and modem.
What cable do I need to run a long (10-20m) extension from the master socket to the Openreach modem? Can I get one free from Plusnet? Free from BT? Buy one from somewhere?
Do I need to call the BT Engineer back? However I want to take the cable into the office which is off the front door, so I will be going under carpet etc....
Cheers
James

[#2]

Mine is just CAT5E with RJ11 connectors crimped on the ends and plugged into the extension socket on the new master faceplate.

[#3]

Thanks I thought that might be the case, but wanted to check first.

[#4]

Hi,
I'm not sure we can get one resupplied after install, I have a feeling not but will ask the question.