Two BT Master Sockets

[#1]

Hi, I have a quick question and was hoping someone would be able to offer some advice.
I've recently moved to a new house which appears to have two BT master sockets.  They both have the split faceplate with a master test socket behind.
I was wondering if this is likely to be an issue and cause problems with broadband speed etc.  I've read conflicting things on whether it's likely to be a problem or not.

[#2]

do they both work as it may be that once there were two lines into the house

[#3]

Yes I've just checked and the other socket is live.  However I lost my broadband connection when the phone was plugged into it for some reason.

[#4]

I assume that the one which works on broadband has a filtered faceplate and hence the other socket has been connected to the phone only wires.
This would mean that there isn't a problem and I suspect that whoever wired up the property had run out of extension sockets so used a spare master instead

[#5]

Ok thanks Jim.  It's weird that whenever I connect a phone to this and get a dialling tone my router goes down though.  I guess I just won't plug anything into it in future

[#6]

Did you try connecting the phone to that second socket using a microfilter?

[#7]

Remove the lower part of the face plates to reveal both test sockets. One of the test sockets should still be live (that's the real master) and the other dead. If they are both still live you've got problems!

[#8]

Also to add to Jelv's comment if both of these are live (after face plates are off) try to make a call out on each line. If one of them cuts you off mid-dial then that was a second line and can be ignored.

[#9]

OK thanks I've connected to the test socket and there's no dial tone so seems it's just connected as an extension socket.  Not sure why it reboots the router when I plug a phone into it though (I did use a microfilter). 
Think I'll just leave well alone 

[#10]

Sometimes just plugging in a phone/microfilter combination causes an SNRM spike which triggers a resync.
And a reminder the clear way to check whether you actually have 2 lines and/or what they are is to dial 17070. You will be told what the circuit is.
How is this second socket actually wired?