For the record, ISP simply stands for:
ISPs are the companies who provide your broadband connection, whether it is mobile 3G or 4G internet, or a fixed-line home connection.
ISPs and BT
The majority of the UK’s land-line infrastructure is owned by BT. If you have phone-line internet (also known as ADSL), the provider you get it from will rent BT’s lines and telephone exchanges. They will then install their own internet-providing software to give you your broadband connection. This is why you have to pay line rental to BT as well as service costs to your provider.
The only companies that are independent of this are mobile phone providers (who provide 3G and 4G internet connections wirelessly through mobile networks) and Virgin Media, who have their own cable infrastructure (having bought it from the NTL Telewest group in 2008).
uSwitch Broadband lists the majority of the best UK internet service providers in the UK for you to compare and contrast, so start your ISP comparison here!