Your BB connection is fine, in itself. You are getting top rate from Infinity 1.
Your issue will be congestion at your local exchange.
As I said, it appears that you have a congestion problem. As licquorice stated in message 10 there is nothing that you can do about it other than just wait for BT to deal with it.
And how long could that take? It's already been almost two months since the broadband was installed and the entire time it has been this poor, on average I'm getting around 5% of a service I'm paying full price for. Surely there should be some sort of compensation if it's not going to be sorted fairly soon.
Generally speaking you only get compensation if you have lost your connection and not just getting slower speeds.
I have notified the moderators of the forum about your problem. Once they have read this they may be able to help. They are a BT UK based team and if they can help they will reply via this thread asking you to contact them via a link. They are very busy at present so once you have replied to them by the link, it can take over 48 hours for them to re-contact you.
It does look like your connection is affected by a capacity issue at the exchange. If you send me in your details I'll be able to take a look at this for you.
You can send me in your details using the "Contact The Mods" link found in my profile.