Unlimited account but downloads throttled

[#1]

I am downloading a large amount of data (torrent, p2p, legal self owned) and the diagnostic started with a clean, maximum, download rate (dlr).
On checking the stats it is now all over the place from near zero dlr to close to maximum (8mbps). The average is c.2mbps maybe a little less.
Will somebody at PN tell me what is going on because this is NOT what I expected.

[#2]

The trouble with torrents is that you are reliant on OTHERS to provide the download speed. Is the torrent you are download well seeded? Are you at a time where they maybe slowing down?
Try a speed test and see if it is full speed.
I don't use torrents much but speed is very variable on them anyway. Things like web/streaming/nttp are full speed for me.

[#3]

I'm not in the office so can't check, but I wonder if the torrent is now seeding and using all the available upload bandwidth. If this happens you can often see that the downloads slow down as the 'ack' packets can't be sent/received due to the upload being saturated. Try limiting the upload speed and see if that helps.

[#4]

Already done, Chris: seeds good.
Speed test gives just under 6mbps.
Different torrent tried: with fewer seeds ran at max dlr. Watching other torrents, the original then speeded up and the new one slowed.
Actually, it's my son who is doing this (himself a PN user elsewhere in the UK until moving house this week pending moving in) so I'll hand this thread over to him.
ITM, my guess is that it's the torrents not PN.