> Demon [1], seems to offer abysmally low bandwidth caps on almost every plan

They're very low on "Home and home office" plans, low on "Business" plans (200GB from 19 quids) and unlimited in the premier section (30 quids).

> and generally low max download speeds (20Mb or less)

It's ADSL, ADSL2+ caps out at 24Mb/s.