Where is the Firewall?
 

I have contactwed Plusnet and this is the reply I received:
"Unfortunately we cannot do this. The restrictions are primarily related to the fact you are on the Plus account which is not geared towards P2P access. We would recoment upgradin to the Premier account. This can be done online"
AS the cost of my present package is £14.99 per month and the upgraded package is £21.99 per month, I have decided not to upgrade.
Using the ports you recommended, I am able to upload for about 2 hours before the firewall blocks me. I then have to wait for about 8 hours before I am able to start uploading again again.

Well at least that confirms the firewall issue is definitely due to PlusNet. Since you're in UK, there are other ISP's there which don't shape bandwidth or block ports. ukbobboy01 has investigated a number of other UK isp's if you're interested in finding out about alternatives.