The "up-to" term used by ISP is proved, once again, to be different from the actual speed provided to subscribers, even on DSL networks (as oppose to DSL carrier usual claims when compared to shared media access services, such as cable or wireless).
"Today’s research found that superfast services offer significantly faster speeds than copper ADSL broadband, with much smaller differences – or no difference – between headline speed claims and actual speeds .. However, over 75 per cent of UK residential broadband connections are currently delivered by copper ADSL telephone lines. The research found that the average download speed received for ADSL ‘up to’ 20Mbit/s and 24Mbit/s ADSL services was 6.6Mbit/s, and more than a third of customers (37 per cent)on these packages received average speeds of 4Mbit/s or less"
See "Consumers benefit from UK broadband speed surge" - here, full document - here and previous report - here.