Master Socket Issue

I've been with Nildram for a while and everything was hunky dorey until Jan this year when my broadband speed dropped to around 160kbps mark. After doing everything I could I called them and logged a fault and after calling and chasing them for over 2 months and doing all the tests they suggested me to do today they've told me the problem *might* be with my master socket faceplate.
Basically when I've got my router plugged in the master socket my Netgear router shows downstream speed as 160kbps but as soon as i plug it in the test socket it jumps up to around 3000kbps mark. Today I did 2 speed tests on this website one with the router plugged in the master socket while the other one when it was in the test socket of the master socket and there was a huge speed difference.
I want to replace the faceplate, is it something I'll be able to do myself? I work in IT so I'm fairly technical but don't know great deal about BT sockets. Also shall I replace it with a like to like faceplate or is there a better product for broadband?
Its my first post on this forum so I hope you guys would help me out. Many Thanks

My understanding is that when you plug into the test socket all the internal extension wiring is disconnected. This seems to indicate you have a problem with your internal extension wiring.

Presumably you do have extension wiring of some sort ? This being the case, it is most likely this that is causing the issue, not the faceplate itself. The first thing to check would be the filters on the other end of the extensions, and also ensure there isn't 'something' plugged in without one (Sky/fax/answer phone/alarms/etc) If this all seems correct, have a read through Yarwells pages.......here, and in particular the stuff about disconnecting ones bell wires.

That's true. There really isn't that much in the faceplate to go wrong.

I've got 5 internal phone ports (boxes) but I don't use any of those except one which has got my home phone plugged in. I'm wondering is it OK if I just plugged in my router and phone in the test socket permanently?
Thanks for all your replies.

You'd be better off finding out where the internal wiring is going wrong (if that is the problem).

I know it's a silly question but you have got a filter on the phone haven't you?

Yes I've got a filter on the phone. It has been working perfectly fine up until January. I had the router plugged into one of the extension sockets and never had a problem. But now even the master socket is playing up. You guys are right, it might be my internal wiring so I think I'll have to spend sometime sorting all that out considering the fact that I've got one extension in almost every single room!!!