PS... Later the same night, (at 5.30am) I tried again to access the
net via braodband. This time, neither my PC nor my Vonage device can
connect. And when I tried to get access via dialup, I find that access
to web sites is extremely slow and I keep losing the connection.

(This is all with my adsl filter still plugged into the hidden socket
inside the cover of the BT master socket.)

Looks like the 'faulty master socket cover' diagnosis was not the
solution....

Cheers,

Jake D