If a BT ADSL engineer has atteneded the premises and failed to get the connection to work then the line should be marked as not available on the number checker. The precise wording is :-

"Your exchange has ADSL broadband.
However, despite an engineer's visit to your premises it has been proved not possible for your telephone line to support broadband service. Please accept our apologies. We are continuing to look for alternative technology solutions and this site will be updated with developments as
they happen."

If an engineer hasn't visited then issues with household wiring may have been overlooked.

People on very long lines would be well advised to start by ordering Home250 from Zen internet - this uses a lower modem speed and has proven to have greater range.