It happens that Broadback formulated :
I got a flyer advertising a good deal. Fine except when I try to do a speed
check I have to log in, they ask for data (BT numbers etc) which I do not
have. How can I overcome this? their help system Is of not help whatsoever!
:-)

How can you test line speed, if you don't have a line?

They can tell you the likely speed you can achieve, based on your
address and choice of broadband type - fibre, copper or FTTC.