You could have an external line fault which is is picking up interference, or perhaps a high resistance connection.
Can you please run a line test and see if it shows a fault condition.
You can do it from here.
i have tryed the line test twice now and all that happens is my broadband drops for 2 mins then comes back..
That is correct it will disconect while the test takes place
Also using FON has no effect on getting Infinity that depends on if your local street cabinet is upgraded from your post it sound as though you are on a different cabinet to those on the other side of the road which is quite common
Thanks anyway, i'll continue to be a frustrated BT customer like hundreds of others.