Where best to start troubleshooting?

My ISP has upgraded me to an ADSL2+ service, which I'm happy with in terms of reliabilty and stability,

However using the speedtester on this site shows my link as having a worse download speed than before the upgrade (although I should probably look at more than just the download speed alone).

So, I want to look into whether there's anything I can do to improve it.

I'm still using a SpeedTouch ST510 v4 modem which is connected via internal wiring to the master socket. That internal wiring is probably a cowboy job, but the computer is in a different room to the master socket.

In turn the master socket doesn't look like an official BT socket. Also when I lost the line recently a BT engineer had to check the line into the house and it would appear that there were two lines, to confuse matters.

Overall I could do with some advice as to where to start looking. From looking at the BT website, BT Total Broadband customers can get an engineer to visit and check wiring, but my broadband is not with BT. Is it worth starting with the line into the house, the master socket and the internal wiring, then the router and finally my ISP?

TIA,

MarkDemon

I'd start by temporarily plugging your modem/router into the master socket to see if the internal wiring is affecting your sync rate or not (disconnect as much non-essential stuff as possible if you haven't got a proper test socket).

See http://www.dslzoneuk.net/socket.php?type=html

As a very quick test you could try forcing your modem/rouer to sync using ADSL rather than ADSL2+. This might bring back your missing sync speed.