Im sorry to argue but PlusNet HAVE bloked the P2P ports on the HOMESURF accounts. Look at this email from them

We are pleased to be able to inform you that a member of our Customer Support
Centre has now returned ticket number [ 16381018 ] to yourself.

The following comment was added to the ticket
Dear Mr Wagner,
The account type you are on "adsl home surf" is a restricted account and all peer 2 peer ports are blocked. This has always been the case however modern software in some cases could get round this. We now have equipment in place which now restricts traffic correctly on your account type that is why you are seeing this occuring. If you wish to have all ports unblocked you will need to check our current product range and select a product on which you could do this. Our £21.99 premier package with a usage allowance of 30Gb would be ok for what you are trying to achieve.