What version of Java are you using (in LW go help > about LW & you'll see)?
Are you sharing a connection with other computers?
How do you have your modem set up (UPnP enabled, port forwarding or neither)? What's the brand & model of the modem?

You could try deleting LW's preferences folder when LW's closed. Points 2 & 3 below will explain how
Fixes for LimeWire

TalkTalk are known to shape bandwidth during certain hours, which will mean a drop in speed. I guess it's possible that they've increased their traffic shaping. Have a look through this thread
http://www.gnutellaforums.com/showth...light=talktalk

Have you tried other p2p apps & are they really slow too? Have you tried going back to the older version of LW to see if speed picks up again?