As djfunkdup says, your best bet for best speed will probably be based on a TalkTalk connection of some sort.
TalkTalk itself may or may not suit you due to it's P2P restrictions, but it will be the cheapest
fast broadband, assuming it does offer ADSL2+ there. Most places it does, just occasionally it is 8Mbps.
More expensive, but with more personal support, you can look at resellers of TalkTalk Wholesale - vivaciti and xilo/uno. Their products are different, so I suggest you contact both. Without a phone number that would be easier than their web sites.
Vivaciti can certainly (at additional cost) get the P2P throttling removed. I don't know the detail of xilo/uno's version.
My broadband basic info/help site - www.robertos.me.uk
My domains,website and mail hosting - Tsohost.
Internet connection - IDNet Home Starter Fibre.
Live BQM.
"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.