This must be a line fault?

Recently my line has been up and down like a yoyo.

I used to connect for weeks on end at 5.6Mb and then things got a little noisy and my sync dropped to 5.1Mb with interleaving on and would stay up for weeks. My attenuation used to be 45db and it is now 50db.

In recent months I have been lucky to hold onto a 4512 sync but in the last week or two things have taken a turn for the worse.

I tried running FAST and the DLM sent my SNR upto 9db - connecting at 4120kbps for 4 days and then dropping down to 3.8Mb.

I decided speed was more important than latency and re-enabled interleaving and now the line is sitting at 3.5Mb after it was initially syncing at 4576kbps.

I'm getting a fair bit of jitter on the connection as soon as the sun goes down.

My question is will BT do anything about this?

They'll probably do nothing, they are under no obligation other than 28Kbps functional internet access and will be that way until 2015 or longer

The ISP may be able to show the historical data to BT wholesale support, but chances of getting someone out to fix things is rare. On the attenuation jump - have you checked that your line has not become ADSL2+ under 21CN in this time frame

My exchange offers absoloutely nothing apart from bog standard IPStream.