Read the small print.
ISP's advertise the maximum connection speed and have disclaimers which state clearly that your specific connection speed will vary because of factors out of their control.
If YOU fail to read this then it is YOUR fault not theirs if you are unhappy with what you get.
If YOU have any common sense you will pick an ISP that has relaxed contractual terms so you can either downgrade or change service to another(cheaper) ISP if you don't get decent connection speed at your location. (E.g why pay for upto12mb when you get 2mb, better to change package/ISP and pay for say upto 8mb).
You can check how far you are from your local exchange, this simple action alone will give you a clue as to what to expect. You live 8km from your exchange and buy an upto 20MB service and only get 4.5mb, well boo hoo, what do you expect? Better to pay for an upto 8mb service and accept the reality of your situation.
Unlimited means unilmited, ISP's should not be able to use this word if their service has any form of shaping or capping. OFCOM should get the cocks out of their mouths and do something about this misrepresentation.
There are some really good ISP's out there who for around £10-20 a month offer "Real Unlimited" internet over ADSL and ADSL2+ (so 8-24Mb/s max) and I tell you now that they are not Pipex, Sky, BT, Talk Talk, Orange, Virgin or any of those large and bastardised companies who do cap you and who do shape your traffic at peak times and who do want to squeeze for every penny but only offer you for a poor service.
My ISP charges me £22 monthly(IP is Static too), I get almost 19Mb/s down and 2Mb/s up. They don't cap me, they don't shape my traffic at peak times, they don't email me with threats of disconnection if I have heavy use for a sustained period, they don't tie me into a 12month contract either and they are very helpful when things do go wrong.
3 Years and very happy. Used BT before that and it was shoddy at best. Use Clueless and Wotless before that and wanted to kill someone. Used BT before C&W when I had ISDN and ended up with a £900 bill for a fault in their modems, again I wanted to kill someone lol.
Avoid Stack-em-high-sell-em-cheap-IPS's they will bend you over and give you what-for.