Hi, thanks for the info. I have this issue, and I'm with Plusnet. I asked about it on their forums yesterday, didn't get any reply of any use really. But I tried the Wirershark guide and on the example it showed it said this:

4. Analysing The Data

The following information shows you how to interpret the data that has been captured by Wireshark.

The screenshot below is a packet capture taken just before and during a http download of a Linux ISO from mirror.ac.uk.
We need to locate a packet that has been sent from the download source to your computer. It is important that we capture traffic that is traveling in this direction (to the customer) as upstream traffic will not have been marked by the Ellacoyas.
Look at the line highlighted in green that shows a packet that has been sent from the IP address 194.80.135.25 to the IP address 192.168.1.2.
192.168.1.2 is a local IP address; 194.80.135.25 is the IP address for mirror.ac.uk as we can see from nslookup:
My connections from 199.xxx are all high priority, but all my connections TO 199.xxx are lowest priority. Why would the guide say to ignore the upoad ones? Is this what's causing lag issues? I tried forwarding ports earlier today, and it wasn't as bad tonight, it may well be coincidence though.